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Review| Volume 41, ISSUE 3, P483-499, September 2020

Testing for SARS-CoV-2 (COVID-19): a systematic review and clinical guide to molecular and serological in-vitro diagnostic assays

      Abstract

      The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its associated coronavirus disease 2019 (COVID-19) pandemic has demanded rapid upscaling of in-vitro diagnostic assays to enable mass screening and testing of high-risk groups, and simultaneous ascertainment of robust data on past SARS-CoV-2 exposure at an individual and a population level. To meet the exponential demand in testing, there has been an accelerated development of both molecular and serological assays across a plethora of platforms. The present review discusses the current literature on these modalities, including nucleic acid amplification tests, direct viral antigen tests and the rapidly expanding laboratory-based and point of care serological tests. This suite of complementary tests will inform crucial decisions by healthcare providers and policy makers, and understanding their strengths and limitations will be critical to their judicious application for the development of algorithmic approaches to treatment and public health strategies.

      Key Words

      Introduction

      In December 2019, an outbreak of an unexplained pneumonia originated from the city of Wuhan, Hubei Province, China (
      • Guan W.J.
      • Ni Z.Y.
      • Hu Y.
      • Liang W.H.
      • Ou C.Q.
      • He J.X.
      • et al.
      Clinical Characteristics of Coronavirus Disease 2019 in China.
      ;
      • Huang X.
      • Wei F.
      • Hu L.
      • Wen L.
      • Chen K.
      Epidemiology and Clinical Characteristics of COVID-19.
      ). After the initial outbreak, a novel coronavirus (severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2]) was quickly identified as the aetiological agent, and the associated disease defined as COVID-19 (an acronym from COrona VIrus Disease, where 19 stands for the year the virus was first detected). The exponential growth of affected individuals led the World Health Organization (WHO) to declare a global pandemic on 11 March 2020 (
      • Huang X.
      • Wei F.
      • Hu L.
      • Wen L.
      • Chen K.
      Epidemiology and Clinical Characteristics of COVID-19.
      ), with 3,002,303 confirmed cases and 208,131 deaths worldwide as of 27 April 2020, and many more anticipated.
      The use of direct molecular diagnostic testing based on sequencing of SARS-CoV-2 has been critical in identifying infected individuals. However, as lockdown measures have begun to bite, there has been a race to develop and approve tests with a different purpose, to assess not current viral infection but rather immunity to severe SARS-CoV-2 to facilitate a return to work. Despite this, antibody testing may also be relevant in the critical evaluation of the disease, including: (i) understanding the kinetics of the immune response to infection; (ii) understanding the immune response relative to disease severity and timeline; (iii) understanding whether cross-reactivity with other coronaviruses (CoV) leads to cross-protection; (iv) clarifying whether infection protects from future infection and how long immunity will last; and (v) determining the correlates of protection that can guide public health measures. In addition to these critical questions, immediate clinical applications include: (i) the diagnosis and triage of patients who seek medical attention in the later phases of the disease; (ii) contact tracing; (iii) stratifying workforces and patients if immunity is shown to be lasting; and (iv) sero-epidemiological studies to understand the extent of COVID-19 spread.
      An understanding of the application and diagnostic performance of the different testing approaches for SARS-Cov-2 is essential in the fight against this pandemic. In the field of reproductive technology, these tests are believed by many to be one of the milestones for recommencing clinical activity. The recent European Society for Human Reproduction and Embryology (www.eshre.eu/Home/COVID19WG) position statement highlighted the current lack of understanding in the field of in-vitro diagnostic assays and in particular serological testing, and the American Society for Reproductive Medicine (www.asrm.org/news-and-publications/covid-19) has called for healthcare providers to be aware of the limitations of these tests. The purpose of this review is to provide an overview of current diagnostic approaches for SARS-CoV-2 and in particular highlight issues with serological testing, with the objective of providing a clear guide to clinicians on the assays currently available.

      Literature search

      A literature search was carried out for studies that focused on the diagnostic and serological testing for SARS-CoV-2, using the keywords “coronavirus”, “severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)” and “COVID-19”. The PubMed, Google Scholar and EMBASE databases were searched without language restrictions from inception through to 16 April 2020 and updated on 15 May 2020. Given the rapidly developing field and rapid dissemination of scientific findings with respect to COVID-19, the preprint servers for both health sciences (medRxiv) and biology (bioRxiv) databases were also searched. Additional journal articles were identified from the bibliographies of included studies. For the main objective of this review, all original studies reporting on the sensitivity and/or specificity of antibodies against SARS-CoV-2 were included in the analysis. More than 20,000 articles have been published on SARS-CoV-2, of which 4182 articles are related to CoV and antibodies or serology. After screening the title and abstract, 887 full-text studies were retrieved, with 65 studies meeting the inclusion criteria and reporting data on test sensitivity and/or specificity, as summarized in Table 1.
      Table 1Summary of the original articles reporting on SARS-CoV-2 antibody testing
      Author, YearDesign of the studyNPopulationCountry of the test populationAntibody usedMethodologyMain findings and/or conclusionsSensitivity (%)Specificity (%)PPVNPV
      PubMed articles
      • Li Z.
      • Yi Y.
      • Luo X.
      • Xiong N.
      • Liu Y.
      • Li S.
      • Sun R.
      • Wang Y.
      • Hu B.
      • Chen W.
      • Zhang Y.
      • Wang J.
      • Huang B.
      • Lin Y.
      • Yang J.
      • Cai W.
      • Wang X.
      • Cheng J.
      • Chen Z.
      • Sun K.
      • Pan W.
      • Zhan Z.
      • Chen L.
      • Ye F.
      Development and Clinical Application of A Rapid IgM-IgG Combined Antibody Test for SARS-CoV-2 Infection Diagnosis.
      Retrospective525397 RNA-positive patients, 128 controlsChinaCommercial assayJiangsu Medomics Medical Technologies, LFIAThe test time was from day 8 to day 33 after symptoms appeared. The IgM–IgG combined assay has better utility and sensitivity than a single IgM or IgG test. Results demonstrate that the IgG–IgM combined antibody test kit can be used as a POC test88.6690.63NANA
      • Xiao D.A.T.
      • Gao D.C.
      • Zhang D.S.
      Profile of Specific Antibodies to SARS-CoV-2: The First Report.
      Prospective34SARS-CoV-2 confirmed patientsChinaCommercial assayShenzhen Yahuilong Biotechnology, chemiluminescence assayAfter 2 weeks from the onset of symptom, all but two subjects had positive results from the test. From the 5th to 7th weeks IgM became negative, while all had high levels of IgG94.1NANANA

      Zhao J., Yuan Q., Wang H., Liu W., Liao X., Su Y., et al. Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease 2019. Clin. Infect. Dis. doi:https://doi.org/10.1093/cid/ciaa344

      Prospective535 samples from 173 subjects173 RNA-positive patientsChinaCommercial assayBeijing Wantai Biological Pharmacy Enterprise, ELISAThe seroconversion rates for Ab, IgM and IgG were 93.1%, 82.7% and 64.7%. The cumulative seroconversion curve showed that the rates for antibody and IgM reached 100% around 1 month of illness100 (>15 days)NANANA
      • Du Z.
      • Zhu F.
      • Guo F.
      • Yang B.
      • Wang T.
      Detection of antibodies against SARS-CoV-2in patients with COVID-19.
      Retrospective60Convalescent patients (6–7 weeks from onset)ChinaCommercial assayELISAAll patients tested positive for IgG against the virus, while 13 patients tested negative for IgM78 IgM

      100 IgG
      NANANA
      • Cassaniti I.
      • Novazzi F.
      • Giardina F.
      • Salinaro F.
      • Sachs M.
      • Perlini S.
      • Bruno R.
      • Mojoli F.
      • Baldanti F.
      Members of the San Matteo Pavia COVID-19 Task Force
      Performance of VivaDiag COVID-19 IgM/IgG Rapid Test is inadequate for diagnosis of COVID-19 in acute patients referring to emergency room department.
      Prospective11030 RNA-positive patients, 50 patients with respiratory symptoms, 30 controlsChinaCommercial assayRapid VivaDiag IgM /IgG immunoassayThe rapid test is not recommended for triage of patients with suspected COVID-19 in the emergency room18.491.787.526.2
      • Guo L.
      • Ren L.
      • Yang S.
      • Xiao M.
      • Chang
      • Yang F.
      • Dela Cruz C.S.
      • Wang Y.
      • Wu C.
      • Xiao Y.
      • Zhang L.
      • Han L.
      • Dang S.
      • Xu Y.
      • Yang Q.
      • Xu S.
      • Zhu H.
      • Xu Y.
      • Jin Q.
      • Sharma L.
      • Wang L.
      • Wang J.
      Profiling Early Humoral Response to Diagnose Novel Coronavirus Disease(COVID-19).
      Prospective208 samples from 140 subjects82 confirmed and 58 probable casesChinaIn-house assayELISA for IgA, IgM and IgGIgA, IgM and IgG were detected in 92.7%, 85.4% and 77.9% of samples from a median time of 5 days from the onset of symptoms75.6 (IgM in confirmed cases)

      93.1 (IgM in probable cases)
      NANANA
      • Jin Y.
      • Wang M.
      • Zuo Z.
      • Fan C.
      • Ye F.
      • Cai Z.
      • Wang Y.
      • Cui H.
      • Pan K.
      • Xu A.
      Diagnostic value and dynamic variance of serum antibody in coronavirus disease 2019.
      Retrospective7643 RNA-positive patients, 33 probable casesChinaCommercial assayShenzhen YHLO Biotech, chemiluminescence assayViral serological testing is an effective means of diagnosing SARS-CoV-2 infection. The positive rate and titre variance of IgG are higher than those of IgM48.1 IgM

      88.9 IgG
      100 IgM

      90.9 IgG
      NANA
      • Pan Y.
      • Zhang D.
      • Yang P.
      • Poon L.L.M.
      • Wang Q.
      Viral load of SARS-CoV-2 in clinical samples.
      Retrospective105105 patientsChinaIn-house assayImmunochromatographyThe positive rates of Ig in the early stage are relatively low and gradually increase during disease progression. The IgM-positive rate rose from 11.1% in early-stage to 74.2% in late-stage disease. The IgG-positive rate in confirmed patients was 3.6% in early-stage and 96.8% in late-stage disease68.6NANANA
      • Padoan A.
      • Sciacovelli L.
      • Basso D.
      • Negrini D.
      • Zuin S.
      • Cosma C.
      • Faggian D.
      • Matricardi P.
      • Plebani M.
      IgA-Ab response to spike glycoprotein of SARS-CoV-2 innpatients with COVID-19: A longitudinal study.
      Retrospective87 samples from 37 subjects37 patientsItalyCommercial assaySnibe, MAGLUM 2000 Plus 2019-nCov IgM and IgG assaysAfter the 11th day from the onset of symptoms, all patients were found to be positive for IgG (100%), while the higher positivity of IgM (88%) was achieved only after the 13th day. The imprecision and repeatability of the test were acceptable88 IgM

      100 IgG
      NANANA
      • Zhong L.
      • Chuan J.
      • Gong B.O.
      • Shuai P.
      • Zhou Y.
      • Zhang Y.
      • et al.
      Detection of serum IgM and IgG for COVID-19 diagnosis.
      Cross-sectional34747 RNA-positive patients, 300 controlsChinaCommercial assayELISA and chemiluminescence detection assayThe ELISA and chemiluminescence methods were consistent in detecting IgG and IgM antibodies by the recombinant N and S proteins of SARS-CoV-297.9 IgM

      95.7 IgG
      99.7 IgM

      85.7 IgG
      NANA
      • Infantino M.
      • Grossi V.
      • Lari B.
      • Bambi R.
      • Perri A.
      • Manneschi M.
      • Terenzi G.
      • Liotti I.
      • Ciotta G.
      • Taddei C.
      • Benucci M.
      • Casprini P.
      • Veneziani F.
      • Fabbri S.
      • Pompetti A.
      • Manfredi M.
      Diagnostic accuracy of an automated chemiluminescentimmunoassay for anti-SARS-CoV-2 IgM and IgG antibodies: an Italian experience.
      Cross-sectional12561 RNA-positive patients and 64 controlsChinaCommercial assayiFlash CLIA, Chemiluminescence assayThe ROC AUC were 0.918 and 0.980 for IgM and IgG anti-SARS CoV-2 antibodies73.3 (IgM)

      76.7 (IgG)
      92.2

      100
      81.5

      NA
      88.1

      90.1
      • Xiang F.
      • Wang X.
      • He X.
      • Peng Z.
      • Yang B.
      • Zhang J.
      • Zhou Q.
      • Ye H.
      • Ma Y.
      • Li H.
      • Wei X.
      • Cai P.
      • Ma W.L.
      Antibody Detection and Dynamic Characteristics in Patients with COVID-19.
      Retrospective216 samples from 109 subjects85 confirmed and 24 suspected casesChinaCommercial assaysZhu Hai LivZon Diagnostics, ELISAThe seropositive rate of IgM increased gradually and notably. IgG was increased sharply on the 12th day after onset. Diagnostic performance calculated from samples obtained after 13 days from the onset77.3 IgM

      83.3 IgG
      100

      95
      100

      94.8
      80

      83.8
      • Lee Y.L.
      • Liao C.H.
      • Liu P.Y.
      • Cheng C.Y.
      • Chung M.Y.
      • Liu C.E.
      • Chang S.Y.
      • Hsueh P.R.
      Dynamics of anti-SARS-Cov-2 IgM and IgG antibodies among COVID-19 patients.
      Retrospective33 samples from 14 subjects, 28 samples from 28 controls14 RNA-positive patients and 28 controlsChinaCommercial assayAlltest, Rapid TestAntibody response varied with different clinical manifestations and disease severity. Patients with symptoms and development of anti-SARSCoV-2 IgM antibodies had a shorter duration of a positive rRT-PCR result and no worsening clinical conditions compared with those without the presence of anti-SARS-CoV-2 IgM antibodies78.6100NANA
      • Long Q.X.
      • Liu B.Z.
      • Deng H.J.
      • Wu G.C.
      • Deng K.
      • Chen Y.K.
      • Liao P.
      • Qiu J.F.
      • Lin Y.
      • Cai X.F.
      • Wang D.Q.
      • Hu Y.
      • Ren J.H.
      • Tang N.
      • Xu Y.Y.
      • Yu L.H.
      • Mo Z.
      • Gong F.
      • Zhang X.L.
      • Tian W.G.
      • Hu L.
      • Zhang X.X.
      • Xiang J.L.
      • Du H.X.
      • Liu H.W.
      • Lang C.H.
      • Luo X.H.
      • Wu S.B.
      • Cui X.P.
      • Zhou Z.
      • Zhu M.M.
      • Wang J.
      • Xue C.J.
      • Li X.F.
      • Wang L.
      • Li Z.J.
      • Wang K.
      • Niu C.C.
      • Yang Q.J.
      • Tang X.J.
      • Zhang Y.
      • Liu X.M.
      • Li J.J.
      • Zhang D.C.
      • Zhang F.
      • Liu P.
      • Yuan J.
      • Li Q.
      • Hu J.L.
      • Chen J.
      • Huang A.L.
      Antibody responses to SARS-CoV-2 in patients with COVID-19.
      Cross-sectional285 patients285 RNA-positive patientsChinaCommercial assayChemiluminescence Bioscience assayThe positive rate of IgG reached 100% around 17–19 days after symptom onset, while the IgM seroconversion rate reached its peak of 94.1% around 20–22 days after symptom onset94 (IgM)

      100 (IgG)
      NANANA
      • Perera R.A.
      • Mok C.K.
      • Tsang O.T.
      • Lv H.
      • Ko R.L.
      • Wu N.C.
      • Yuan M.
      • Leung W.S.
      • Chan J.M.
      • Chik T.S.
      • Choi C.Y.
      • Leung K.
      • Chan K.H.
      • Chan K.C.
      • Li K.C.
      • Wu J.T.
      • Wilson I.A.
      • Monto A.S.
      • Poon L.L.
      • Peiris M.
      Serological assays for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), March 2020.
      Retrospective51 samples from 24 patients24 RNA-positive patientsChinaIn-house assayELISAIgG and IgM were reliably positive after 29 days from illness onset with no detectable cross-reactivity in age-stratified controls74100NANA
      • Qu J.
      • Wu C.
      • Li X.
      • Zhang G.
      • Jiang Z.
      • Li X.
      • Zhu Q.
      • Liu L.
      Profile of IgG and IgM antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
      Retrospective347 samples from 41 patients and 38 samples from controls41 RNA-positive patients and 38 controlsChinaCommercial assayYHLO Biotech, chemiluminescence assayThe majority of the patients developed robust antibody responses between 17 and 23 days after illness onset87.8 (IgM)

      97.6 (IgG)
      NANANA
      • Shen B.
      • Zheng Y.
      • Zhang X.
      • Zhang W.
      • Wang D.
      • Jin J.
      • Lin R.
      • Zhang Y.
      • Zhu G.
      • Zhu H.
      • Li J.
      • Xu J.
      • Ding X.
      • Chen S.
      • Lu R.
      • He Z.
      • Zhao H.
      • Ying L.
      • Zhang C.
      • Lv D.
      • Chen B.
      • Chen J.
      • Zhu J.
      • Hu B.
      • Hong C.
      • Xu X.
      • Chen J.
      • Liu C.
      • Zhou K.
      • Li J.
      • Zhao G.
      • Shen W.
      • Chen C.
      • Shao C.
      • Shen X.
      • Song J.
      • Wang Z.
      • Meng Y.
      • Wang C.
      • Han J.
      • Chen A.
      • Lu D.
      • Qian B.
      • Chen H.
      • Gao H.
      Clinical evaluation of a rapid colloidal gold immunochromatography assay for SARS-Cov-2 IgM/IgG.
      Prospective150 patients150 suspected cases, of whom 97 were RNA positiveChinaCommercial assayShanghai Outdo Biotech, rapid immunochromatography testThe colloidal gold immunochromatography assay for SARS-Cov-2-specific IgM/IgG antibody shows the potential for a useful rapid diagnosis test for COVID-1971969764
      • Zhao R.
      • Li M.
      • Song H.
      • Chen J.
      • Ren W.
      • Feng Y.
      • Gao G.F.
      • Song J.
      • Peng Y.
      • Su B.
      • Guo X.
      • Wang Y.
      • Chen J.
      • Li J.
      • Sun H.
      • Bai Z.
      • Cao W.
      • Zhu J.
      • Zhang Q.
      • Sun Y.
      • Sun S.
      • Mao X.
      • Su J.
      • Chen X.
      • He A.
      • Gao W.
      • Jin R.
      • Jiang Y.
      • Sun L.
      Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
      Retrospective48169 affected subjects and 412 controlsChinaIn-house assayELISAThe overall accuracy of the ELISA test was 97.3%97.597.5NANA
      • Cai X.F.
      • Chen J.
      • Hu J.L.
      • Long Q.X.
      • Deng H.J.
      • Fan K.
      • Liao P.
      • Liu B.Z.
      • Wu G.C.
      • Chen Y.K.
      • Li Z.J.
      • Wang K.
      • Zhang X.L.
      • Tian W.G.
      • Xiang J.L.
      • Du H.X.
      • Wang J.
      • Hu Y.
      • Tang N.
      • Lin Y.
      • Ren J.H.
      • Huang L.Y.
      • Wei J.
      • Gan C.Y.
      • Chen Y.M.
      • Gao Q.Z.
      • Chen A.M.
      • He C.L.
      • Wang D.X.
      • Hu P.
      • Zhou F.C.
      • Huang A.L.
      • Liu P.
      • Wang D.Q.
      A Peptide-based Magnetic Chemiluminescence Enzyme Immunoassay for Serological Diagnosis of Coronavirus Disease 2019 (COVID-19).
      Retrospective276 samples from 276 subjects, 200 samples from 200 controls276 RNA-positive patients, and 200 healthy controlsChinaIn-house assayChemiluminescence assayCombining immunoassay with real-time RT-PCR might enhance the diagnostic accuracy of COVID-1957.2 (IgM)

      71.4 (IgG)
      NANANA
      • Döhla M.
      • Boesecke C.
      • Schulte B.
      • Diegmann C.
      • Sib E.
      • Richter E.
      • Eschbach-Bludau M.
      • Aldabbagh S.
      • Marx B.
      • Eis-Hübinger A.M.
      • Schmithausen R.M.
      • Streeck H.
      Rapid point-of-care testing for SARS-CoV-2 in a community screening setting shows low sensitivity.
      ProspectiveSamples from 49 symptomatic patients22 RNA-positive and 27 RNA-negative patientsGermanyCommercial assayRapid testThe rapid test was substantially inferior to the RT-qPCR testing and should therefore be used for neither individual risk assessment nor decisions on public health measures36.488.972.763.1
      • Hoffman T.
      • Nissen K.
      • Krambrich J.
      • Rönnberg B.
      • Akaberi D.
      • Esmaeilzadeh M.
      • Salaneck E.
      • Lindahl J.
      • Lundkvist Å.
      Evaluation of a COVID-19 IgM and IgG rapid test; an efficient tool for assessment of past exposure to SARS-CoV-2.
      Cross-sectionalSamples from 153 subjects29 RNA-positive patients and 124 controlsChinaCommercial assayZhejiang Orient Gene Biotech, rapid COVID testThe test is suitable for assessing previous virus exposure, although negative results may be unreliable during the first weeks after infection69 (IgM)

      93 (IgG)
      100 (IgM)

      99.2 (IgG)
      100 (IgM)

      96.4 (IgG)
      93.2 (IgM)

      98.4 (IgG)
      • Hou H.
      • Wang T.
      • Zhang B.
      • Luo Y.
      • Mao L.
      • Wang F.
      • Wu S.
      • Sun Z.
      Detection of IgM and IgG antibodies in patients with coronavirus disease 2019.
      Retrospective338 subjects338 RNA-positive patientsChinaCommercial AssayYHLO, ELISAQuantitative detection of IgM and IgG antibodies against SARS-CoV-2 quantitatively has potential significance for evaluating the severity and prognosis of COVID-1982.7 (IgM)

      88 (IgG)
      NANANA
      • Imai K.
      • Tabata S.
      • Ikeda M.
      • Noguchi S.
      • Kitagawa Y.
      • Matuoka M.
      • Miyoshi K.
      • Tarumoto N.
      • Sakai J.
      • Ito T.
      • Maesaki S.
      • Tamura K.
      • Maeda T.
      Clinical evaluation of an immunochromatographic IgM/IgG antibody assay and chest computed tomography for the diagnosis of COVID-19.
      Retrospective139 samples from 112 patients and 48 controls112 RNA-positive patients and 48 controlsArtron, CanadaCommercial assayArtton, One Step IgM/IgG Rapid TestImmunoassay had low sensitivity during the early phase of infection, and thus immunoassay alone is not recommended for initial diagnostic testing for COVID-1940NANANA
      • Lippi G.
      • Salvagno G.L.
      • Pegoraro M.
      • Militello V.
      • Caloi C.
      • Peretti A.
      • Gaino S.
      • Bassi A.
      • Bovo C.
      • Lo Cascio G.
      Assessment of immune response to SARS-CoV-2 withfully automated MAGLUMI 2019-nCoV IgG and IgM chemiluminescence immunoassays.
      Prospective48 patients48 RNA-positive patientsSnibe Cehmiluminescence Maglumi, Italy Euroimmun, ItalyCommercial assaysSnibe, Chemiluminescence MAGLUMI; EUROIMMUN, ELISAThe results of MAGLUMI are well aligned with those of the EUROIMMUN test10 (<5days)

      100 (>10 days)
      NANANA
      • Pan Y.
      • Li X.
      • Yang G.
      • Fan J.
      • Tang Y.
      • Zhao J.
      • Long X.
      • Guo S.
      • Zhao Z.
      • Liu Y.
      • Hu H.
      • Xue H.
      • Li Y.
      Serological immunochromatographic approach in diagnosis with SARS-CoV-2 infected COVID-19 patients.
      Retrospective86 samples from 67 cases67 RNA-positive patientsChinaCommercial assayZhuhai Livzon Diagnostic, rapid lateral flow assaysSerology may be considered a supplementary approach in clinical diagnosis11 (<7 days)

      92 (7–14 days)

      96 (>14 days)
      NANANA
      • Spicuzza L.
      • Montineri A.
      • Manuele R.
      • Crimi C.
      • Pistorio M.P.
      • Campisi R.
      • Vancheri C.
      • Crimi N.
      Reliability and usefulness of a rapid IgM-IgG antibody test for the diagnosis of SARS-CoV-2 infection: A preliminary report.
      Cross-sectional41 subjects27 RNA-positive patients, 7 symptomatic RNA-negative patients and 7 controlsChinaCommercial assayBeijing Diagreat Biotechnologies, rapid lateral flow assayAntibody test is quite reliable and useful as it has the advantage of being a POC test that gives a response within minutes8393NANA
      • Sun B.
      • Feng Y.
      • Mo X.
      • Zheng P.
      • Wang Q.
      • Li P.
      • Peng P.
      • Liu X.
      • Chen Z.
      • Huang H.
      • Zhang F.
      • Luo W.
      • Niu X.
      • Hu P.
      • Wang L.
      • Peng H.
      • Huang Z.
      • Feng L.
      • Li F.
      • Zhang F.
      • Li F.
      • Zhong N.
      • Chen L.
      Kinetics of SARS-CoV-2 specific IgM and IgG responses in COVID-19 patients.
      Cross-sectional130 samples from 38 patients, 16 samples from 16 controls38 RNA-positive patients and 16 controlsChinaIn-house assayELISAIgM and IgG increased gradually after symptom onset and can be used for detection of SARS-CoV-2 infection. Analysis of the dynamics of IgG may help to predict prognosis75 (after 1 week)

      94.7 (after 2 weeks)

      100 (after 3 weeks)
      NANANA
      • To K.K.
      • Tsang O.T.
      • Leung W.S.
      • Tam A.R.
      • Wu T.C.
      • Lung D.C.
      • et al.
      Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study.
      Cross-sectional16 patients16 RNA-positive patientsChinaIn-house assayELISASerological assay can complement RT-qPCR for diagnosis88 (IgM)

      94 (IgG)
      NANANA
      • Xie J.
      • Ding C.
      • Li J.
      • Wang Y.
      • Guo H.
      • Lu Z.
      • Wang J.
      • Zheng C.
      • Jin T.
      • Gao Y.
      • He H.
      Characteristics of patients with coronavirus disease (COVID-19) confirmed using an IgM-IgG antibody test.
      Prospective56 patients56 symptomatic patientsChinaCommercial assayYHLO Biological Technology, chemiluminescence assayA combination of nucleic acid and Ig testing is a more accurate approach for diagnosing COVID-1993.7 (IgM)

      100 (IgG)
      NANANA
       Yonh G et al., 2020Retrospective76 samples from 38 patients38 symptomatic patientsChinaCommercial assayRapid assay GICA kitAntibody detection could be used as an effective indicator of the virus in the absence of viral RNA50 (IgM)

      92.1 (IgG)
      NANANA
      • Bryan A.
      • Pepper G.
      • Wener M.H.
      • Fink S.L.
      • Morishima C.
      • Chaudhary A.
      • Jerome K.R.
      • Mathias P.C.
      • Greninger A.L.
      Performance Characteristics of the Abbott Architect SARS-CoV-2 IgG Assay and Seroprevalence in Boise, Idaho.
      Cross-sectional6001 subjects1020 controls and 125 patients. 4856 subjects from the general populationUSACommercial assayAbbott, chemiluminescence SARS-CoV-2 IgG testThis study demonstrates excellent analytical performance of the Abbott SARS-CoV2 test as well as the limited circulation of the virus in the western USA53.1 (day 7)

      82.4 (day 10)

      96.9 (day 14)

      100 (day 17)
      99.9NANA
      • Demey B.
      • Daher N.
      • François C.
      • Lanoix J.P.
      • Duverlie G.
      • Castelain S.
      • Brochot E.
      Dynamic profile for the detection of anti-SARS-CoV-2 antibodies using four immunochromatographic assays.
      Prospective21 subjects21 RNA-positive patientsFranceCommercial assaysFour rapid lateral flow assaysImmunochromatographic tests for detection of the virus may have a role in the diagnosis of COVID-199-24 (day 5)

      67–82 (day 10)

      100 (day 15)
      99.8NANA
      • Jääskeläinen A.J.
      • Kekäläinen E.
      • Kallio-Kokko H.
      • Mannonen L.
      • Kortela E.
      • Vapalahti O.
      • Kurkela S.
      • Lappalainen M.
      Evaluation of commercial and automated SARS-CoV-2 IgG and IgA ELISAs using coronavirus disease (COVID-19) patient samples.
      Retrospective77 subjects40 RNA-positive patients and 37 controlsGermanyCommercial assayEUROIMMUN, ELISAThe median time after onset of symptoms was 12 days (13 patients, range 5–20 days) for detection of IgG and 11 days (24 patients, range 5–20 days) for detection of IgANA91.9 (IgG)

      73 (IgA)
      NANA
       Montesinos J et al., 2020Retrospective400 subjects272 controls and 128 RNA-positive patientsGermanyCommercial assaysMAGLUMI, chemiluminescence; EUROIMMUN, ELISA; rapid assayThe sensitivity of the tests increased with time from onset of symptoms64.3 (MAGLUMI)

      84.4 (EUROIMMUN)

      70 (rapid assay)
      99

      100
      NANA
      • Tang M.S.
      • Hock K.G.
      • Logsdon N.M.
      • Hayes J.E.
      • Gronowski A.M.
      • Anderson N.W.
      • Farnsworth C.W.
      Clinical Performance of Two SARS-CoV-2 Serologic Assays.
      Retrospective201 subjects48 patients and 153 controlsAbbott USAEuroimmun USACommercial assaysAbbott, chemiluminescence assay; EUROIMMUN, ELISABoth assays have poor sensitivity during the first days of the disease. Abbott tests generally performed better than the EUROIMMUN testAbbott:

      0 (<3 days)

      30 (3–7 days)

      47.8 (8–13 days)

      93.8 (>14 days)

      EUROIMMUN:

      0 (<3 days)

      25 (3–7 days)

      56.5 (8–13 days)

      85.4 (>14 days)
      99.4 (Abbott)NANA
      MedRxiv articles
      • Wang X.
      • Guo X.
      • Xin Q.
      • Chu Y.
      • Li J.
      • Pan Y.
      • Feng Y.
      • Wang Q.
      Neutralizing Antibodies Responses to SARS-CoV-2 in COVID-19 Inpatients and Convalescent Patients.
      Prospective study with longitudinal follow-up117 samples in 70 subjectsInpatients and convalescent patientsChinaIn-house assayModified cytopathogenic assayThe seropositivity rate reached up to 100.0% within 20 days after onset. Patients with a worse clinical classification had a higher antibody titre100NANANA
       Garcia PF et al., 2020Prospective16355 RNA-positive patients, 63 RNA-negative patients, 45 controlsChinaCommercial AssayAllTest, COV 19 IgG IgM immunoassayThe sensitivity of the test was 73.9% after 2 weeks from the onset of symptoms73.9100NANA
      • Lassaunière R.
      • Frische A.
      • Harboe Z.
      • Nielsen A.
      • Fomsgaard A.
      • Krogfelt K.
      • Jørgensen C.
      Evaluation of nine commercial SARS-CoV-2 immunoassays.
      Cross-sectional11130 SARS-CoV-2 patients, 10 healthy controls, 71 patients with respiratory diseases other than SARS-CoV-2DenmarkCommercial assays3 ELISA tests and 6 POC lateral flow testsThe diagnostic performance of the commercial assays analysed may vary65–90 (ELISA)

      83–93 (POC)
      96–100 (ELISA)

      80–100 (POC)
      82–100 (ELISA)

      100 (POC)
      89–98 (ELISA)

      74–92 (POC)
      • Yangchun F.
      Optimize Clinical Laboratory Diagnosis of COVID-19 from Suspect Cases by Likelihood Ratio of SARS-CoV-2 IgM and IgG antibody.
      Cross-sectional294186 RNA-positive patients, 98 RNA-negative patientsChinaCommercial assayELISAAntibody testing has a very good diagnostic performance in identifying positive subjects96.1 (IgG)92.4 (IgG)96.09 (IgG)90.1 (IgG)

      Liu R., Liu X., Han H., Shereehn M.A., Niu Z., Li D. et al. The comparative superiority of IgM-IgG antibody test to real-time reverse transcriptase PCR detection for SARS-CoV-2 infection diagnosis 2020 doi: https://doi.org/10.1101/2020.03.28.20045765

      Retrospective133Samples from patientsChinaCommercial AssayYHLO, IG detection kitIn symptomatic patients, IgM was superior to RT-PCR in detecting affected subjects. The positive rate for IgM was 79.55% in moderate cases, 82.69% 156 in severe cases and 72.97% in critical cases. The IgG antibody test positive rate was 93.18% in moderate cases, 100.00% in severe cases and 97.30% in critical cases78.95 (IgM)

      93.18 (IgG)
      NANANA
      • Liu Y.
      • Liu Y.
      • Diao B.
      • Ren F.
      • Wang Y.
      • Ding J.
      • Huang O.
      Diagnostic Indexes of a Rapid IgG/IgM Combined Antibody Test for SARS-CoV-2.
      Retrospective179Patients, RNA positive (n = 90) and RNA negative (n = 89)ChinaCommercial assayRapid immunoassayThe accuracy of the antibody testing increased over time (from 40% in the first week from onset of symptoms to 93.9% 2 weeks later)85.69195.182.7
      • Yong G.
      • Yi Y.
      • Tuantuan L.
      • Xiaowu W.
      • Xiuyong L.
      • Ang L.
      • Mingfeng H.
      Evaluation of the auxiliary diagnostic value of antibody assays for the detection of novel coronavirus (SARS-CoV-2).
      Retrospective38PatientsChinaCommercial assayRapid assay GICA IgG IgM detection kitThe accuracy of the test 8 days after the onset of symptoms5092.1NANA
      • Lin D.
      • Liu L.
      • Zhang M.
      • Hu Y.
      • Yang Q.
      • Guo J.
      • Dai Y.
      • Xu Y.
      • Cai Y.
      • Chen X.
      • Huang K.
      • Zhang Z.
      Evaluations of serological test in the diagnosis of 2019 1 novel coronavirus (SARS-CoV-2) infections during the COVID-19 outbreak.
      Retrospective14979 RNA-positive patientsChinaCommercial assayDarui Biotech, ELISAThe sensitivity of the test increased with time from onset of the disease82.297.5NANA
      • Lou B.
      • Li T.D.
      • Zheng S.F.
      • Su Y.Y.
      • Li Z.Y.
      • Liu W.
      • Yu F.
      • Ge S.X.
      • Zou Q.D.
      • Yuan Q.
      • Lin S.
      • Hong C.M.
      • Yao X.Y.
      • Zhang X.J.
      • Wu D.H.
      • Zhou G.L.
      • Hou W.H.
      • Li T.T.
      • Zhang Y.L.
      • Zhang S.Y.
      • Fan J.
      • Zhang J.
      • Xia N.S.
      • Chen Y.
      Serology characteristics of SARS-CoV-2 infection since the exposure and post symptoms onset.
      Cross-sectional38080 RNA-positive patients. 300 healthy controlsChinaCommercial assayELISA and lateral flow assayThe overall seroconversion rate was 98.8% at a median of 9 days from the onset of disease98.894.3NANA
      • Liu L.
      • Liu W.
      • Wang S.
      • Zheng S.
      A preliminary study on serological assay for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 238 admitted hospital patients.
      Cross-sectional238238 patients, 153 of them RNA-positive. 120 controlsChinaCommercial assayLizhu, ELISAAntibody detection should be used as a major viral diagnostic test for patients with symptoms for more than 10 days. The combination of ELISA and RT-PCR assays will greatly improve detection efficacy, even in the early stage of infection81.5NANANA
      • Bendavid E.
      • Mulaney B.
      • Sood N.
      • Shah S.
      • Ling E.
      • Bromley-Dulfano R.
      • et al.
      COVID-19 Antibody Seroprevalence in Santa Clara County, California.
      Cross-sectional33003300 subjects from the general populationChinaCommercialPremier Biotech, LFIAThe population prevalence of COVID-19 in Santa Clara, CA, ranged from 2.49% to 4.16%, 50- to 85-fold more than reported cases80.399.5NANA
      • Paradiso A.V.
      • De Summa S.
      • Loconsole D.
      • Procacci V.
      • Sallustio A.
      • Centrone F.
      • Silvestris N.
      • Cafagna V.
      • De Palma G.
      • Tufaro A.
      • Garrisi V.
      • Chironna M.
      Clinical meanings of rapid serological assay in patients tested for SARS-Co2 RT-PCR.
      Prospective191191 symptomatic patientsChinaCommercialRapid VivaDiag IgM /IgG immunoassayThe performance of the test at the onset of symptoms was low. Sensitivity was 66.7% 15 days later3089NANA
      • Jia X.
      • Zhang P.
      • Tian Y.
      • Wang J.
      • Zeng H.
      • Wang J.
      • Liu J.
      • Chen Z.
      • Zhang L.
      • He H.
      • He K.
      • Liu Y.
      Clinical significance of IgM and IgG test for diagnosis of highly suspected COVID-19 infection.
      Retrospective5959 suspected patients, 24 of whom were RNA positiveChinaCommercial assayDiagreat, immunofluorescence assayIgM and IgG may provide a quick, simple and accurate detection method for suspected COVID-19 patients87.5NANANA
      • Zhang J.
      • Liu J.
      • Li N.
      • Liu Y.
      • Ye R.
      • Qin X.
      • Zheng R.
      Serological detection of 2019-nCoV respond to the epidemic: A useful complement to nucleic acid testing.
      Retrospective736228 suspected cases, 3 positive. 508 controlsChinaCommercial assayShenzhen Yahuilong Biotechnology, chemiluminescence assayDetection of specific antibodies in patients with fever can be a good complement to nucleic acid diagnosis for early diagnosis of suspected cases1009775100
      • Xiang J.
      • Yan M.
      • Li H.
      • Liu T.
      • Lin C.
      • Huang S.
      • Shen C.
      Evaluation of Enzyme-Linked Immunoassay and Colloidal Gold-Immunochromatographic Assay Kit for Detection of Novel Coronavirus (SARS-Cov-2) Causing an Outbreak of Pneumonia (COVID-19).
      Retrospective189154 patients, 35 controlsChinaCommercial assaysZhu Hai Liv Zon Diagnostics, ELISA and GICA assaysThere is no difference between the sensitivity of ELISA and GICA assay; both are simple and fast, and the results can be used for clinical reference87.3 (ELISA)

      82.4 (GICA)
      100 (ELISA)

      100 (GICA)
      NANA

      Hu Q., Cui X., Liu X., Peng B., Jiang J., Wang X. et al., The production of antibodies for SARS-CoV-2 and its clinical implication 2020 doi: https://doi.org/10.1101/2020.04.20.20065953

      Prospective993 samples from 221 subjects221 hospitalized patientsChinaCommercial assayBioScience, chemiluminescence assayIgG and IgM antibodies examined every 3 days revealed increasing antibody levels that peaked on day 19–21. SARS-CoV-2 IgG and IgM antibody testing should be combined with RT-PCR as an early diagnosis method73.6 IgM

      97.8 IgG

      (day 13–18 after the onset)
      NANANA

      Ma H., Zeng W., He H., Zhao D., Yang Y., Jiang D., et al., COVID-19 diagnosis and study of serum SARS-CoV-2 specific IgA, IgM and IgG by a quantitative and sensitive immunoassay 2020 doi: https://doi.org/10.1101/2020.04.17.20064907

      Cross-sectional216 samples from 87 subjects87 RNA-positive patientsChinaIn-house assayChemiluminescenceMeasuring SARS-CoV-2 specific antibodies IgA, IgM and IgG in serum provides better serological testing with improved sensitivity and specificity98.6 IgA

      96.8 IgM

      96.8 IgG
      98.1 IgA 92.3 IgM 99.8 IgGNANA
      • Qian C.
      • Zhou M.
      • Cheng F.
      • Lin X.
      • Gong Y.
      • Xie X.
      • et al.
      Development and Multicenter Performance Evaluation of The First Fully Automated SARS-CoV-2 IgM and IgG Immunoassays.
      Prospective, multicentric2061 subjects from 10 hospitals972 non-COVID patients, 586 controls, 503 RNA-positive patientsChinaCommercial assayShenzhen YHLO Biotech, chemiluminescence assayThe assay showed a coefficient of variation of less than 5%. SARS-CoV-2 IgM and IgG showed clinical specificity of over 97% and 86.54% for suspected cases85.8 IgM

      96.6 IgG
      99 IgM

      99 IgG
      NANA
       National COVID testing Scientific Advisory Board, 2020Cross-sectional18240 RNA-positive patients, 142 controlsUKCommercial assaysElisa and 9 commercial LFIAThe performance of current LFIA devices is inadequate for most individual patient applications. ELISA can be calibrated to be specific for detecting and quantifying SARSCoV-2 IgM and IgG and is highly sensitive for IgG from 10 days following symptom onset85 (ELISA)

      55-70 (LFIA versus RT-PCR)
      100 (ELISA)

      65–85 (LFIA versus ELISA)
      NANA

      Burbelo P.D., Francis X.R., Morishima C., Rawlings S., Smith D., Das S. et al., Detection of Nucleocapsid Antibody to SARS-CoV-2 is More Sensitive than Antibody to Spike Protein in COVID-19 Patients 2020 https://doi.org/10.1101/2020.04.20.20071423

      Cross-sectional10068 patients, 32 controlsUSAIn-house assayLuciferase 44 immunoprecipitation assay systems to the nucleocapsid (NP) and spike proteins (SP)Antibody to the nucleocapsid protein of SARS-CoV-2 is more sensitive than 56 spike protein antibody for detecting early infection100 (anti-NP)

      91 (anti-SP)
      100 (anti-NP)

      100 (anti-SP)
      NANA
      • Adams E.R.
      • Augustin Y.
      • Byrne R.L.
      • Clark D.J.
      • Cocozza M.
      • Cubas-Atienzar A.I.
      • et al.
      Rapid development of COVID-19 rapid diagnostics for low resource settings: accelerating delivery through transparency, responsiveness, and open collaboration.
      Retrospective834 samples270 positive samples, 564 negative samplesUKCommercial assayMologic, ELISAThe ELISA tested had good diagnostic performance8897NANA

      Meyer B., Torriani G., Yerly S., Mazza L., Calame A., Arm-Vernez I. et al. Validation of a commercially available SARS-CoV-2 serological Immunoassay medRxiv 2020.05.02.20080879; doi: https://doi.org/10.1101/2020.05.02.20080879

      Retrospective357 subjects176 controls, 181 RNA-positive patientsGermanyCommercial assayEUROIMMUN, ELISAThe assay displays an optima diagnostic accuracy using IgG, with no obvious gain from IgA serology8210010046

      Norman M., Gilboa T., Ogata F.A., Maley A.M., Cohen L., Cay Y. et al. Ultra-Sensitive High-Resolution Profiling of Anti-SARS-CoV-2 Antibodies for Detecting Early Seroconversion in COVID-19 Patients medRxiv 2020.04.28.20083691; doi: https://doi.org/10.1101/2020.04.28.20083691

      Retrospective81 subjects81 subjectsUSAIn-house assaySingle Molecular Array (SIMOA)The SIMOA serological platform provides a powerful analytical tool86100NANA
      • Tuaillon E.
      Detection of SARS-CoV-2 antibodies using commercial assays and seroconversion patterns in hospitalized patients.
      Prospective5838 RNA-positive patients and 20 controlsEuroimmun, GermanyIdVet, FranceCommercial assayElisa by EUROIMMUN and IdVet and 5 rapid lateral flow testsThe second week of COVID-19 seems to be the best period for assessing the sensitivity of commercial serological assays86.7 (ELISA)

      80–93.3 (rapid tests)
      80–85 (ELISA)

      65–100 (rapid tests)
      NANA
      • Wajnberg A.
      • Mansour M.
      • Leven E.
      • Bouvier N.M.
      • Patel G.
      • Firpo A.
      • et al.
      Humoral immune response and prolonged PCR positivity in a cohort of 1343 SARS-CoV 2 patients in the New York City region.
      Prospective1343 subjects1343 symptomatic subjects, of whom 624 were RNA-positiveRoche, USACommercial assayRoche, chemiluminescence assayThe vast majority of confirmed COVID-19 patients seroconvert, potentially providing immunity to reinfection82NANANA
      • Wan Y.
      • Li Z.
      • Wank K.
      • Li T.
      • Liao P.
      Performance verification of detecting COVID-19 specific antibody by using four chemiluminescence immunoassay systems.
      Retrospective18050 RNA-positive patients and 130 controlsChinaCommercial assayFour chemiluminescence assay systemsSystems for CoVID-2019 IgM/IgG antibody test may perform differently26–9278–99NANA
      • Xiao T.
      • Wang Y.
      • Yuan J.
      • Ye H.
      • Wei L.
      • Wang H.
      • et al.
      Early viral clearance and antibody kinetics of COVID-19 among asymptomatic carriers.
      Retrospective56 subjects56 RNA-positive patients (33 symptomatic and 23 asymptomatic)ChinaCommercial assayChemiluminescence microparticle immunoassayAsymptomatic carriers were found to have a lower initial viral load, undetectable IgM and moderate levels of IgG90.9

      95.5

      90.9

      63.2
      NANANA

      Zhou Q., Zhu D., Yan H., Quan J., Kuang Z., Zhang, W. et al., A preliminary study on analytical performance of serological assay for SARS-CoV-2 IgM/IgG and application in clinical practice medRxiv 2020.05.05.20092551; doi: https://doi.org/10.1101/2020.05.05.20092551

      Retrospective419 subjects19 RNA-positive patients and 400 controlsChinaCommercial assayChemiluminescenceViral serological testing is an effective means of detecting SARS-CoV-2 infection91.6NANANA
      • Ozturk T.
      • Howell C.
      • Benameur K.
      • Ramonell R.P.
      • Cashman K.
      Pirmohammed S Cross-sectional IgM and IgG profiles in SARS-CoV-2 infection.
      Cross-sectional148 subjects32 RNA-positive patients, 116 controlsUSACommercial assayGenScript, ELISAThere is a complex relationship between antibody levels, disease severity and time since symptom onset, so caution is needed in using serological assay to inform public policies88.992.3NANA
      • Rosado J.
      • Cockram C.
      • Merkling H.
      • Demeret C.
      • Meola A.
      • Kerneis S.
      Serological signatures of SARS-CoV-2 infection: Implications for antibody-based diagnostics.
      Retrospective594259 RNA-positive patients, 335 controlsFranceIn-house assayMultiplex serological assay using a serological signature of IgG to four antigensSerological signatures based on antibody responses to multiple antigens can provide more accurate and robust serological classification of individuals with previous SARS-CoV-2 infection96.199.1NANA
      Searched up to 15 May 15. Case reports and review articles have not been included.
      AUC, area under the curve; ELISA, enzyme-linked immunosorbent assay; GICA, gold immunochromatographic assay; Ig; LFIA, lateral flow immunoassay; NA, not available; NPV, negative predictive value; PPV, positive predictive value; qPCR, quantitative PRC; POC, point of care; ROC, receiver operating characteristic; RT-PCR, reverse transcription-PCR; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

      Coronaviral genome and structure

      CoV belong to the subfamily Coronavirinaein the family of Coronaviridae of the order Nidovirales. In this subfamily four genera are included Alphacoronavirus, Betacoronavirus, Gammacoronavirus and Deltacoronavirus. The genome of the virus is a single-stranded positive-sense RNA (+ssRNA) (around 30 kb in size) with a 5′-cap structure and 3′-poly-A tail. The genome and subgenomes of a typical CoV may present six, or even more, open reading frames (ORF). The first ORF (ORF1a/b) encompasses approximately 66% of the whole genome and encodes 16 non-structural proteins (nsp1–16), which are mainly involved in the replication of CoV. Other ORF encompassing one-third of the genome near the 3′-terminus encode the main structural proteins: spike (S), membrane (M), envelope (E) and nucleocapsid (N) proteins (
      • Chen Y.
      • Liu Q.
      • Guo D.
      Emerging coronaviruses: Genome structure, replication, and pathogenesis.
      ).
      The different CoV exhibit 54% identity of the whole RNA, with 58% exhibiting identity for the non-structural proteins coding region and 43% identity for the structural protein coding region. Sequence analysis shows that the new CoV incorporates the typical genome structure of CoV and belongs to the cluster of betac-CoV that includes bat-SARS-like (SL)-ZC45, bat-SL ZXC21, SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV). Based on the phylogenetic tree of CoV, 2019-nCoV is more closely related to bat-SL-CoV ZC45 and bat-SL-CoV ZXC21 and more distantly related to SARS-CoV (
      • Chen Y.
      • Liu Q.
      • Guo D.
      Emerging coronaviruses: Genome structure, replication, and pathogenesis.
      ).
      Four principal structural proteins are essential for assembly of the virion and its associated infective capacity. Homotrimers of S proteins make up the spikes on the viral surface, which are responsible for attachment to receptors on the host cells. The M protein has three transmembrane domains and shapes the virions, promotes membrane curvature and covers the nucleocapsid. The E protein participates in virus assembly and release, and is involved in viral pathogenesis. The N protein presents two domains, both of which can bind virus RNA genome via different mechanisms. The N protein binds to non-structural protein 3 (nsp3) protein to help tether the genome to the replication–transcription complex and package the encapsidated genome into virions. The N protein is also an antagonist of interferon and viral encoded repressor of RNA interference, which may be beneficial for viral replication.

      Diagnostic tests for the SARS-CoV-2

      On 22 May 2019, the database held by the Foundation for Innovative New Diagnostics, which is the WHO Collaborating Centre for Laboratory Strengthening and Diagnostic Technology Evaluation, contained 560 SARS-CoV-2 laboratory tests for the diagnosis of COVID-19. These comprised 273 molecular assays and 287 immunoassays. Excluding those intended for research use only, 152 of these are molecular assays and 211 immunoassays are CE-marked for in-vitro diagnostic devices. There are principally two types of tests available for COVID-19: viral tests and antibody tests. The viral tests are direct tests as they are designed to detect the virus and therefore reflect current infection. In contrast, the antibody tests are indirect tests, as they do not detect the virus, but rather ascertain established seroconversion to previous infection, or early seroconversion to ongoing infection.

      Direct tests

      The recommended test for diagnosis of SARS-CoV-2 infection involves detection of viral RNA using nucleic acid amplification tests (NAAT), such as reverse transcription (RT)-PCR (www.ecdc.europa.eu). In areas with widespread community transmission of SARS-CoV-2 and when laboratory resources are limited, detection by RT-PCR of a single discriminatory target is considered sufficient. There are still, however, specific technical considerations for laboratory testing, including specimen collection (variable collection methods), which samples to collect (upper or lower respiratory tract biospecimens, or other samples), time of collection in relation to the course of disease, and the availability of different laboratory test methods and kits (not all of which may be standardized or approved by authorities such as the US Food and Drug Administration). Then there are infrastructure considerations: are the approved laboratory facilities and trained manpower available, can the methodology be rapidly scaled up, and how are test results interpreted and false negatives excluded?
      These issues have been faced by the whole scientific community, with a collective response to develop guidance. The currently used protocol was developed and optimized for the detection of the novel CoV at the Charité University Hospital, Geneva, Switzerland in collaboration with several other laboratories in Germany, the Netherlands, China, France, the UK and Belgium (
      • Corman V.M.
      • Landt O.
      • Kaiser M.
      • Molenkamp R.
      • Meijer A.
      • Chu D.K.
      • et al.
      Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR.
      ). Additionally, the existing protocol was further optimized by the Centers for Disease Control (CDC) in the USA through the comprehensive comparison and validation of alternative kits available for nucleic acid extraction and the use of alternative probe and primer sets for efficient SARS-CoV-2 detection in clinical samples (www.cdc.gov/coronavirus). Similar approaches are being undertaken by other national authorities as they continue to scale up provision for laboratories not using CE-marked assays (www.england.nhs.uk/coronavirus/).
      The importance and variability of specimen collection was initially highlighted from comparison of positive rates from pharyngeal, nasal, blood, sputum, faeces, urine and bronchoalveolar lavage fluid specimens and fibrobronchoscope brush biopsy of patients with confirmed COVID-19 (
      • Zou L.
      • Ruan F.
      • Huang M.
      • Liang L.
      • Huang H.
      • Hong Z.
      • Yu J.
      • Kang M.
      • Song Y.
      • Xia J.
      • Guo Q.
      • Song T.
      • He J.
      • Yen H.L.
      • Peiris M.
      • Wu J.
      SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients.
      ). At present the CDC recommend collecting and testing an upper respiratory specimen, with a nasopharyngeal specimen being the preferred choice for swab-based SARS-CoV-2 testing. When collection of a nasopharyngeal swab is not possible, the following are acceptable alternatives: an oropharyngeal specimen, a nasal mid-turbinate specimen (using a flocked tapered swab), an anterior nares (nasal swab) specimen (using a flocked or spun polyester swab) or a nasopharyngeal wash/aspirate or nasal aspirate specimen. For individuals having invasive procedures, lower respiratory tract specimens are also recommended if available. Although the virus can be detected in other specimens, such as blood and stools, these have been generally less reliable than respiratory specimens.
      At present it is recommended that specimens should be collected as soon as possible once a decision has been made to pursue SARS-CoV-2 testing, regardless of the time of symptom onset. The viral load in throat swabs is greatest at the time of viral onset and decreases monotonically thereafter (
      • To K.K.
      • Tsang O.T.
      • Leung W.S.
      • Tam A.R.
      • Wu T.C.
      • Lung D.C.
      • et al.
      Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study.
      ;
      • Zou L.
      • Ruan F.
      • Huang M.
      • Liang L.
      • Huang H.
      • Hong Z.
      • Yu J.
      • Kang M.
      • Song Y.
      • Xia J.
      • Guo Q.
      • Song T.
      • He J.
      • Yen H.L.
      • Peiris M.
      • Wu J.
      SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients.
      ). Analysis of these temporal dynamics suggests that viral shedding may begin 2–3 days before the appearance of the first symptoms, facilitating pre-symptomatic or asymptomatic transmission (
      • He X.
      • Lau E.H.Y.
      • Wu P.
      • Deng X.
      • Wang J.
      • Hao X.
      • et al.
      Temporal dynamics in viral shedding and transmissibility of COVID-19.
      ). CoV have a number of molecular targets within their +ssRNA genome that can be used for RT-PCR assays. The WHO has provided primers for the genes that encode the structural proteins of the viral envelope (E) and the nucleocapsid (N), and for the RNA-dependent RNA polymerase (RdRp), which is a key part of the virus's replication machinery that makes copies of its RNA genome (
      • Corman V.M.
      • Landt O.
      • Kaiser M.
      • Molenkamp R.
      • Meijer A.
      • Chu D.K.
      • et al.
      Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR.
      ). However, there has been no demonstration that any one of these three sequences (E, N or RdRP) might offer an advantage for clinical diagnostic testing, with different targets being preferred by different authorities. For example, the Public Health England assay employs two probes against RdRp; one is a Pan Sarbeco-probe that will detect 2019-nCoV, SARS-CoV and bat-SARS-related CoV, while the second probe is specific to 2019-NCoV. Continued refinement of these NAAT assays is ongoing to facilitate their upscaling, while maintaining laboratory safety, a low cost and a high sensitivity (
      • Won J.
      • Lee S.
      • Park M.
      • Kim T.Y.
      • Park M.G.
      • Choi B.Y.
      • Kim D.
      • Chang H.
      • Kim V.N.
      • Lee C.J.
      Development of a Laboratory-safe and Low-cost Detection Protocol for SARS-CoV-2 of the Coronavirus Disease 2019 (COVID-19).
      ).

      Detection of isolated viral antigens

      Great efforts have been made in order to develop tests for the rapid detection of SARS-CoV-2 antigens. Antigen detection tests are designed to directly detect viral particles in biological samples such as nasopharyngeal secretions. Several rapid antigen tests have been proposed (
      • Diao B.
      • Wen K.
      • Chen J.
      • Liu Y.
      • Yuan Z.
      • Han C.
      • Chen J.
      • Pan Y.
      • Chen L.
      • Dan Y.
      • Wang J.
      • Chen Y.
      • Deng G.
      • Zhou H.
      • Wu Y.
      Diagnosis of Acute Respiratory Syndrome Coronavirus 2 Infection by Detection of Nucleocapsid Protein.
      ); however, the principal concerns are the false-negative rate due to either a low or variable viral load, and the variability in sampling, the latter having the potential to further compound the problem in cases with low viral titres, thereby increasing the false-negative rate (
      • Tang Y.W.
      • Schmitz J.E.
      • Persing D.H.
      • Stratton C.W.
      The Laboratory Diagnosis of COVID-19 Infection: Current Issues and Challenges.
      ).
      Diao and colleagues (
      • Diao B.
      • Wen K.
      • Chen J.
      • Liu Y.
      • Yuan Z.
      • Han C.
      • Chen J.
      • Pan Y.
      • Chen L.
      • Dan Y.
      • Wang J.
      • Chen Y.
      • Deng G.
      • Zhou H.
      • Wu Y.
      Diagnosis of Acute Respiratory Syndrome Coronavirus 2 Infection by Detection of Nucleocapsid Protein.
      ) have reported preliminary results from the use of a fluorescence immunochromatographic assay for detecting the N protein of SARS-CoV-2 in both nasopharyngeal swab samples and urine from 239 participants, with comparison to NAAT testing where the intersection of the amplification curve and diagnostic threshold line (cycle threshold [Ct] value) was set at either ≤30 or ≤40 (
      • Diao B.
      • Wen K.
      • Chen J.
      • Liu Y.
      • Yuan Z.
      • Han C.
      • Chen J.
      • Pan Y.
      • Chen L.
      • Dan Y.
      • Wang J.
      • Chen Y.
      • Deng G.
      • Zhou H.
      • Wu Y.
      Diagnosis of Acute Respiratory Syndrome Coronavirus 2 Infection by Detection of Nucleocapsid Protein.
      ). With a higher viral load in the sample, the prespecified Ct value may be lower, as fewer replication cycles are required to achieve a detectable signal; however, with a low viral load, a greater number of replication cycles (higher Ct value) will be required for a detectable signal to be attained. For this assay with a prevalence of 87%, although the positive predictive value (PPV) was 100%, the negative predictive value (NPV) was 32% for a Ct ≤40, increasing to 97% for patients with a higher viral load as demonstrated by a Ct ≤30. This would suggest that, at present, this assay would only be useful in excluding those with high viral loads. Whether alternative approaches as previously suggested for influenza viruses in children including the use of colloidal gold-labelled immunoglobulin (Ig) G as the detection reagent (
      • Li Z.
      • Yi Y.
      • Luo X.
      • Xiong N.
      • Liu Y.
      • Li S.
      • Sun R.
      • Wang Y.
      • Hu B.
      • Chen W.
      • Zhang Y.
      • Wang J.
      • Huang B.
      • Lin Y.
      • Yang J.
      • Cai W.
      • Wang X.
      • Cheng J.
      • Chen Z.
      • Sun K.
      • Pan W.
      • Zhan Z.
      • Chen L.
      • Ye F.
      Development and Clinical Application of A Rapid IgM-IgG Combined Antibody Test for SARS-CoV-2 Infection Diagnosis.
      ), to increase the sensitivity of rapid antigen tests for respiratory viruses, are feasible is still under consideration, with monoclonal antibodies specifically against SARS-CoV-2 under development. Further validation of this technique and similar approaches in larger populations including asymptomatic cases is warranted. Consideration of approaches to try to concentrate antigen and amplify the detection phase are, however, likely to be needed for these methods to have any clinical utility (
      • Loeffelholz M.J.
      • Tang Y.W.
      Laboratory diagnosis of emerging human coronavirus infections – the state of the art.
      ).
      At the time of writing (25 April 2020), the non-governmental organization Foundation for Innovative New Diagnostics (https://www.finddx.org/) has listed four CE-marked rapid SARS-CoV-2 antigen detection tests, which are primarily lateral flow immunochromatographic assays based on the presence of a colloid gold conjugate pad and a membrane strip pre-coated with antibodies specific to SARS-CoV-2 antigens on a test line. If SARS-CoV-2 antigens are present in the specimen withdrawn from a nasopharyngeal swab, a visible band appears on the test line as antibody–antigen–antibody gold conjugate complex forms. The evaluation of these diagnostic tests has, however, been limited, and their CE mark means that the manufacturers state that they conform with the relevant EU legislation, but they may still not be available to purchase. According to European Union Directive 98/79/EC for in-vitro diagnostic devices, in order to affix the CE mark to COVID-19 diagnostic devices to be used by health professionals, the manufacturer has to specify device performance characteristics and self-declare conformity with the safety and performance requirements listed in the Directive. In addition, self-tests intended to be used by patients themselves must also be assessed by a third-party body (a notified body), which for these tests has yet to happen.
      Although direct antigen tests are being registered by several health authorities, the sensitivity of these tests is lower than that of RT-PCR, with previous antigen-detecting enzyme-linked immunosorbent assays (ELISA) developed for SARS-CoV having limits of detection of 50 pg/ml (
      • Che X.Y.
      • Qiu L.W.
      • Pan Y.X.
      • Wen K.
      • Hao W.
      • Zhang L.Y.
      • Wang Y.D.i.
      • Liao Z.Y.
      • Hua X.
      • Cheng V.C.C.
      • Yuen K.Y.
      Sensitive and Specific Monoclonal Antibody-Based Capture Enzyme Immunoassay for Detection of Nucleocapsid Antigen in Sera from Patients with Severe Acute Respiratory Syndrome.
      ;
      • Di B.
      • Hao W.
      • Gao Y.
      • Wang M.
      • Wang Y.
      • Di Q.i.u.
      • et al.
      Monoclonal Antibody-Based Antigen Capture Enzyme-Linked Immunosorbent Assay Reveals High Sensitivity of the Nucleocapsid Protein in Acute-Phase Sera of Severe Acute Respiratory Syndrome Patients.
      ). Furthermore, clarification of their specificity for SARS-CoV-2 is awaited, given the potential for cross-reaction with other human CoV. Despite these limitations, the chief advantages of antigen tests, including their rapidity (10–30 min compared with hours for NAAT testing), ease of interpretation and limited technical skill and infrastructure required compared with NAAT-based testing, continue to make them worth pursuing. However, experience with influenza antigen testing invites caution as these tests may have low sensitivity and specificity; moreover, as noted, false–negatives rate will be critical (
      • Tang Y.W.
      • Schmitz J.E.
      • Persing D.H.
      • Stratton C.W.
      The Laboratory Diagnosis of COVID-19 Infection: Current Issues and Challenges.
      ). Their greatest utility if they come to fruition may be in symptomatic patients, when the viral load will be at its greatest, to enable accurate triage.

      Building an indirect test for SARS-CoV-2: serological testing

      In contrast to NAAT-based testing, where as soon as the sequence is known, a diagnostic test can be built, the diagnostic technology and methodology underlying the development of serological tests is quite different, with a substantially longer timeline to obtain a robust product that is suitable for routine deployment. The principal difference is that antibody tests require identification of distinct proteins that form the viral coat, with elucidation of which proteins are most divergent from previous CoV proteins, then identification of specific antibodies to these proteins that are part of the acquired immune response to viral exposure, and finally testing to ensure that there is limited cross-reactivity with antibodies developed to other historical CoV.
      With the previous two CoV, a variety of assays encompassing different methodologies were developed, including ELISA, chemiluminescence, western blotting, protein microarray and immunofluorescence platforms. However, only ELISA and chemiluminescence were deemed suitable for clinical application because of costs, time-to-results, relative simplicity and ability to scale to very large throughput. It is these platforms that are once again being examined for detection of antibodies to SARS-CoV-2.

      Appraisal of test performance

      Appropriate thresholds for sensitivity and specificity of an antibody test depend on its purpose and must be considered prior to implementation. For diagnosis in symptomatic patients, high sensitivity is required (generally ≥90%). In this context, a slight reduction in specificity may be acceptable as some false-positive results may be tolerated, provided other potential diagnoses are considered and there is acceptance that overdiagnosis may result in unnecessary interventions that, for SARS-CoV-2, may include quarantining. However, if antibody tests were deployed as an individual-level approach to inform release from social isolation and return to normal activities, high specificity would be essential, as false-positive results would return non-immune individuals to risk of exposure. It is with these purposes in mind that the UK Medicines and Healthcare products Regulatory Agency set a minimum 98% specificity threshold for flow immunoassays (LFIA). This is particularly challenging, particularly given the scale of validation study required for a suitable candidate LFIA, because to demonstrate a high specificity if the true underlying value were 98%, 1000 negative controls would be required to estimate the specificity of an assay to ±1% with approximately 90% power.
      As part of the evaluation of test performance, the influence of population prevalence also needs to be considered, acknowledging that this is at present rapidly changing (
      • Brenner H.
      • Gefeller O.
      Variation of sensitivity, specificity, likelihood ratios and predictive values with disease prevalence.
      ). This can be considered as the proportion of all positive tests that are wrong, as well as the number of incorrect positive tests per 1000 people tested. For example, for a point of care (POC) test with 70% sensitivity and 98% specificity, the proportion of positive tests that are wrong is 35% at 5% population seroprevalence (19 false positives/1000 tested), 13% at 20% seroprevalence (16 false positives/1000 tested) and 3% at 50% seroprevalence (10 false positives/1000 tested).
      According to available data, the prevalence of seropositivity is still low. The prevalence of antibodies to SARS-CoV-2 among a high risk category such as healthcare personnel is 5.9% in Utah, USA (
      • Madsen T.
      • Levin N.
      • Niehus K.
      • Law K.
      • Mayer J.
      • Chapman M.
      • Johnson A.
      • Hartsell S.
      Prevalence of IgG antibodies to SARS-CoV-2 among emergency department employees.
      ), 5.4% in Lyon, France (
      • Solodky M.L.
      • Galvez C.
      • Russias B.
      • Detourbet P.
      • N'Guyen-Bonin V.
      • Herr A.L.
      • Zrounba P.
      • Blay J.Y.
      Lower detection rates of SARS-COV2 antibodies in cancer patients vs healthcare workers after symptomatic COVID-19.
      ), 17.3% in Trieste (

      Comar M., Brumat M., Concas M.P., Argentini G., Bianco A., Bicego L. et al. COVID-19 experience: first Italian survey on healthcare staff members from a Mother-Child Research hospital using combined molecular and rapid immunoassays test 2020 doi: https://doi.org/10.1101/2020.04.19.20071563

      ), 5.25% in Padua (
      • Tosato F.
      • Pelloso M.
      • Gallo N.
      • Giraudo C.
      • Llanaj G.
      • Cosma C.
      • et al.
      2020 Severe Acute Respiratory Syndrome Coronavirus 2 Serology in Asymptomatic Healthcare Professionals: Preliminary Experience of a Tertiary Italian Academic Center.
      ) and 1.5% in Bari, Italy (
      • Paradiso A.V.
      • De Summa S.
      • Loconsole D.
      • Procacci V.
      • Sallustio A.
      • Centrone F.
      • Silvestris N.
      • Cafagna V.
      • De Palma G.
      • Tufaro A.
      • Garrisi V.
      • Chironna M.
      Clinical meanings of rapid serological assay in patients tested for SARS-Co2 RT-PCR.
      ), 1.6% in Germany (
      • Korth J.
      • Wilde B.
      • Dolff S.
      • Anastasiou O.E.
      • Krawczyk A.
      • Jahn M.
      • Cordes S.
      • Ross B.
      • Esser S.
      • Lindemann M.
      • Kribben A.
      • Dittmer U.
      • Witzke O.
      • Herrmann A.
      SARS-CoV-2-specific antibody detection in healthcare workers in Germany with direct contact to COVID-19 patients.
      ) and 2.6% in Barcelona, Spain (
      • Tuaillon E.
      Detection of SARS-CoV-2 antibodies using commercial assays and seroconversion patterns in hospitalized patients.
      ). In the general population it has been reported as being 0.13% in Rio Grand do Sul, Brazil (
      • Silveira M.
      • Barros A.
      • Horta B.
      • Pellanda L.
      • Victora G.
      • Dellagostin O.
      • et al.
      Repeated population-based surveys of antibodies against SARS-CoV-2 in Southern Brazil.
      ), 1.5% in Santa Clara, California (
      • Bendavid E.
      • Mulaney B.
      • Sood N.
      • Shah S.
      • Ling E.
      • Bromley-Dulfano R.
      • et al.
      COVID-19 Antibody Seroprevalence in Santa Clara County, California.
      ), 1.79 % in Idaho (
      • Bryan A.
      • Pepper G.
      • Wener M.H.
      • Fink S.L.
      • Morishima C.
      • Chaudhary A.
      • Jerome K.R.
      • Mathias P.C.
      • Greninger A.L.
      Performance Characteristics of the Abbott Architect SARS-CoV-2 IgG Assay and Seroprevalence in Boise, Idaho.
      ) and 7.1% in Atlanta, USA (
      • Zou J.
      • Bretin A.
      • Gewirtz A.
      Antibodies to SARS/CoV-2 in arbitrarily-selected Atlanta residents.
      ), 1.2% in Edinburgh, Scotland (
      • Thompson C.
      • Grayson N.
      • Paton R.S.
      • Lourenco J.
      • Penman B.S.
      • Lee L.
      • et al.
      Neutralising antibodies to SARS coronavirus 2 in Scottish blood donors – a pilot study of the value of serology to determine population exposure.
      ), 3% in Paris, France (
      • Grzelak L.
      • Temmam S.
      • Planchais C.
      • Demeret C.
      • Huon C.
      • Guivel F.
      • et al.
      SARS-CoV-2 serological analysis of COVID-19 hospitalized patients, pauci-symptomatic individuals and blood donors.
      ), 1.7% in Denmark (
      • Erikstrup C.
      • Hother C.E.
      • Pdersen O.B.V.
      • Molbak K.
      • Skov R.L.
      • Holm D.K.
      • et al.
      Estimation of SARS-CoV-2 infection fatality rate by real-time antibody screening of blood donors.
      ), 3.3% in Kobe, Japan (
      • Doi A.
      • Iwata K.
      • Kuroda H.
      • Hasuike T.
      • Nasu S.
      • Kanda A.
      • Nagao T.
      • Nishioka H.
      • Tomii K.
      • Morimoto T.
      • Kihara Y.
      Estimation of seroprevalence of novel coronavirus disease (COVID-19) using preserved serum at an outpatient setting in Kobe, Japan: A cross-sectional study.
      ), 9.6% in Wuhan, China (
      • Wu X.
      • Fu B.
      • Chen L.
      • Feng Y.
      Serological tests facilitate identification of asymptomatic SARS-CoV-2 infection in Wuhan, China.
      ) and 21% in Guilan, Iran (
      • Shakiba M.
      • Nazari S.
      • Mehrabian F.
      • Rezvani S.
      • Ghasempour Z.
      • Heidarzadeh A.
      Seroprevalence of COVID-19 virus infection in Guilan province, Iran.
      ). Large-scale seroprevalence studies are ongoing, but understanding the background rate is essential for accurate interpretation of diagnostic tests.
      The potential risk of a test providing false reassurance and release from being sheltered for non-immune individuals can therefore be widely based on the underlying seroprevalence, and this still assumes antibody positivity as a correlate of protective immunity, which may be incorrect.

      Dynamics of seroconversion

      Understanding viral and host interactions during the acute and convalescent phases is critical to be able to understand both the timing of initial seroconversion after exposure to SARS-CoV-2 and the subsequent duration of antibodies. However, at present the studies regarding seroconversion are being developed in parallel to the assays, limiting some conclusions. The data do suggest that seroconversion after exposure to SARS-CoV-2 is very similar to that after other acute viral infections, with IgG concentration beginning to rise as IgM concentrations reach a plateau (Figure 1). However, observations have shown that IgM and IgA growth is relatively slow related to other respiratory viruses, which has been suggested to contribute to the heterogeneous pathogenicity of SARS-CoV-2 in COVID-19 patients (
      • Zhao R.
      • Li M.
      • Song H.
      • Chen J.
      • Ren W.
      • Feng Y.
      • Gao G.F.
      • Song J.
      • Peng Y.
      • Su B.
      • Guo X.
      • Wang Y.
      • Chen J.
      • Li J.
      • Sun H.
      • Bai Z.
      • Cao W.
      • Zhu J.
      • Zhang Q.
      • Sun Y.
      • Sun S.
      • Mao X.
      • Su J.
      • Chen X.
      • He A.
      • Gao W.
      • Jin R.
      • Jiang Y.
      • Sun L.
      Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
      ).
      Figure 1
      Figure 1The time relationship between viral load, symptoms and positivity on diagnostic tests. The onset of symptoms (day 0) is usually 5 days after infection (day –5). At this early stage corresponding to the window or asymptomatic period, the viral load could be below the RT-PCR threshold and the test may give false-negative results. The same is true at the end of the disease, when the patient is recovering. Seroconversion may usually be detectable between 5–7 days and 14 days after the onset of symptoms; therefore, in the first phase of the disease, the serological tests are more likely to give false-negative results. The dotted black line in the graph illustrates the sensitivity of the chemiluminescent assay as derived from the data sheet of a commercial test (Abbott Diagnostics, USA). Ig, immunoglobulin; RT-PCR, reverse transcription-PCR; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.
      The most comprehensive study to date of seroconversion assessed 173 patients affected by COVID-19 using an assay developed to detect antibodies against the receptor binding domain of the S protein of SARS-CoV-2 (
      • Zhao R.
      • Li M.
      • Song H.
      • Chen J.
      • Ren W.
      • Feng Y.
      • Gao G.F.
      • Song J.
      • Peng Y.
      • Su B.
      • Guo X.
      • Wang Y.
      • Chen J.
      • Li J.
      • Sun H.
      • Bai Z.
      • Cao W.
      • Zhu J.
      • Zhang Q.
      • Sun Y.
      • Sun S.
      • Mao X.
      • Su J.
      • Chen X.
      • He A.
      • Gao W.
      • Jin R.
      • Jiang Y.
      • Sun L.
      Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
      ). The median seroconversion times of total antibody, IgM and IgG were 11, 12 and 14 days (
      • Zhao R.
      • Li M.
      • Song H.
      • Chen J.
      • Ren W.
      • Feng Y.
      • Gao G.F.
      • Song J.
      • Peng Y.
      • Su B.
      • Guo X.
      • Wang Y.
      • Chen J.
      • Li J.
      • Sun H.
      • Bai Z.
      • Cao W.
      • Zhu J.
      • Zhang Q.
      • Sun Y.
      • Sun S.
      • Mao X.
      • Su J.
      • Chen X.
      • He A.
      • Gao W.
      • Jin R.
      • Jiang Y.
      • Sun L.
      Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
      ). The respective seroconversion rates for total antibody, IgM and IgG were 93.1%, 82.7% and 64.7% (
      • Zhao R.
      • Li M.
      • Song H.
      • Chen J.
      • Ren W.
      • Feng Y.
      • Gao G.F.
      • Song J.
      • Peng Y.
      • Su B.
      • Guo X.
      • Wang Y.
      • Chen J.
      • Li J.
      • Sun H.
      • Bai Z.
      • Cao W.
      • Zhu J.
      • Zhang Q.
      • Sun Y.
      • Sun S.
      • Mao X.
      • Su J.
      • Chen X.
      • He A.
      • Gao W.
      • Jin R.
      • Jiang Y.
      • Sun L.
      Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
      ), with the cumulative seroconversion curve suggesting that the rate for total antibody and IgM reached 100% 30 days after the onset. These studies have also highlighted the temporal nature of testing as, despite all patients subsequently being confirmed as COVID-19 positive, in the early phase of illness (within 7 days since the onset) the NAAT test only exhibited 66.7% sensitivity, with the antibody assays having an even lower positive rate of 38.3% (
      • Zhao R.
      • Li M.
      • Song H.
      • Chen J.
      • Ren W.
      • Feng Y.
      • Gao G.F.
      • Song J.
      • Peng Y.
      • Su B.
      • Guo X.
      • Wang Y.
      • Chen J.
      • Li J.
      • Sun H.
      • Bai Z.
      • Cao W.
      • Zhu J.
      • Zhang Q.
      • Sun Y.
      • Sun S.
      • Mao X.
      • Su J.
      • Chen X.
      • He A.
      • Gao W.
      • Jin R.
      • Jiang Y.
      • Sun L.
      Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
      ). However, the sensitivity of antibody overtook that of RNA testing from day 8 after symptom onset and reached over 90% across day 12 after onset. Among samples from patients in the later phase (day 15–39 after onset), the sensitivities for total antibody, IgM and IgG were 100.0%, 94.3% and 79.8%, respectively. In contrast, RNA was detectable in only 45.5% of samples from days 15–39. In a separate small series of nine cases, seroconversion occurred after 7 days in 50% of patients (after 14 days in all) but was not followed by a rapid decline in viral load (
      • Wölfel R.
      • Corman V.M.
      • Guggemos W.
      • Seilmaier M.
      • Zange S.
      • Müller M.A.
      • Niemeyer D.
      • Jones T.C.
      • Vollmar P.
      • Rothe C.
      • Hoelscher M.
      • Bleicker T.
      • Brünink S.
      • Schneider J.
      • Ehmann R.
      • Zwirglmaier K.
      • Drosten C.
      • Wendtner C.
      Virological assessment of hospitalized patients with COVID-2019.
      ). An analysis of 285 patients further supports IgG seroconversion within 19 days after symptom onset (
      • Long Q.X.
      • Liu B.Z.
      • Deng H.J.
      • Wu G.C.
      • Deng K.
      • Chen Y.K.
      • Liao P.
      • Qiu J.F.
      • Lin Y.
      • Cai X.F.
      • Wang D.Q.
      • Hu Y.
      • Ren J.H.
      • Tang N.
      • Xu Y.Y.
      • Yu L.H.
      • Mo Z.
      • Gong F.
      • Zhang X.L.
      • Tian W.G.
      • Hu L.
      • Zhang X.X.
      • Xiang J.L.
      • Du H.X.
      • Liu H.W.
      • Lang C.H.
      • Luo X.H.
      • Wu S.B.
      • Cui X.P.
      • Zhou Z.
      • Zhu M.M.
      • Wang J.
      • Xue C.J.
      • Li X.F.
      • Wang L.
      • Li Z.J.
      • Wang K.
      • Niu C.C.
      • Yang Q.J.
      • Tang X.J.
      • Zhang Y.
      • Liu X.M.
      • Li J.J.
      • Zhang D.C.
      • Zhang F.
      • Liu P.
      • Yuan J.
      • Li Q.
      • Hu J.L.
      • Chen J.
      • Huang A.L.
      Antibody responses to SARS-CoV-2 in patients with COVID-19.
      ). Collectively, these data suggest that there is a role for both tests depending on where the patient is on their infection journey, with the combined use of NAAT and antibody tests markedly improving the sensitivity of a pathogenic diagnosis for COVID-19 patients in different phases of the illness.
      With respect to antibody titres and disease severity, critically ill hospitalized patients have been reported to exhibit significantly higher antibody titre values than non-critical patients in some (
      • Long Q.X.
      • Liu B.Z.
      • Deng H.J.
      • Wu G.C.
      • Deng K.
      • Chen Y.K.
      • Liao P.
      • Qiu J.F.
      • Lin Y.
      • Cai X.F.
      • Wang D.Q.
      • Hu Y.
      • Ren J.H.
      • Tang N.
      • Xu Y.Y.
      • Yu L.H.
      • Mo Z.
      • Gong F.
      • Zhang X.L.
      • Tian W.G.
      • Hu L.
      • Zhang X.X.
      • Xiang J.L.
      • Du H.X.
      • Liu H.W.
      • Lang C.H.
      • Luo X.H.
      • Wu S.B.
      • Cui X.P.
      • Zhou Z.
      • Zhu M.M.
      • Wang J.
      • Xue C.J.
      • Li X.F.
      • Wang L.
      • Li Z.J.
      • Wang K.
      • Niu C.C.
      • Yang Q.J.
      • Tang X.J.
      • Zhang Y.
      • Liu X.M.
      • Li J.J.
      • Zhang D.C.
      • Zhang F.
      • Liu P.
      • Yuan J.
      • Li Q.
      • Hu J.L.
      • Chen J.
      • Huang A.L.
      Antibody responses to SARS-CoV-2 in patients with COVID-19.
      ;
      • Zhao R.
      • Li M.
      • Song H.
      • Chen J.
      • Ren W.
      • Feng Y.
      • Gao G.F.
      • Song J.
      • Peng Y.
      • Su B.
      • Guo X.
      • Wang Y.
      • Chen J.
      • Li J.
      • Sun H.
      • Bai Z.
      • Cao W.
      • Zhu J.
      • Zhang Q.
      • Sun Y.
      • Sun S.
      • Mao X.
      • Su J.
      • Chen X.
      • He A.
      • Gao W.
      • Jin R.
      • Jiang Y.
      • Sun L.
      Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
      ) but not all studies. In the previous epidemics of SARS-CoV and MERS-CoV, antibody titres were positively associated with disease severity (
      • Choe P.G.
      • Perera R.A.P.M.
      • Park W.B.
      • Song K.H.
      • Bang J.H.
      • Kim E.S.
      • et al.
      MERS-CoV Antibody Responses 1 Year after Symptom Onset, South Korea, 2015.
      ;
      • Okba N.M.A.
      • Raj V.S.
      • Widjaja I.
      • GeurtsvanKessel C.H.
      • de Bruin E.
      • Chandler F.D.
      • et al.
      Sensitive and Specific Detection of Low-Level Antibody Responses in Mild Middle East Respiratory Syndrome Coronavirus Infections.
      ). In a limited case series (n = 57 confirmed SARS-CoV-2 cases), six patients with detectable viral RNA in the blood were at increased risk of severe disease progression compared with those with low titres, but unfortunately the authors did not measure antibody titres (
      • Chen W.
      • Lan Y.
      • Yuan X.
      • Deng X.
      • Li Y.
      • Cai X.
      • Li L.
      • He R.
      • Tan Y.
      • Deng X.
      • Gao M.
      • Tang G.
      • Zhao L.
      • Wang J.
      • Fan Q.
      • Wen C.
      • Tong Y.
      • Tang Y.
      • Hu F.
      • Li F.
      • Tang X.
      Detectable 2019-CoV viral RNA in blood is a strong indicator for the further clinical severity.
      ). Clarification is awaited of whether even in previously healthy individuals a high viral titre and/or high antibody titre can predict disease severity and likely progression.

      Diagnostic performance of the immunoassays

      Our extensive search identified 24 peer-reviewed articles (
      • Xiao D.A.T.
      • Gao D.C.
      • Zhang D.S.
      Profile of Specific Antibodies to SARS-CoV-2: The First Report.
      ;

      Zhao J., Yuan Q., Wang H., Liu W., Liao X., Su Y., et al. Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease 2019. Clin. Infect. Dis. doi:https://doi.org/10.1093/cid/ciaa344

      ;
      • Du Z.
      • Zhu F.
      • Guo F.
      • Yang B.
      • Wang T.
      Detection of antibodies against SARS-CoV-2in patients with COVID-19.
      ;
      • Guo L.
      • Ren L.
      • Yang S.
      • Xiao M.
      • Chang
      • Yang F.
      • Dela Cruz C.S.
      • Wang Y.
      • Wu C.
      • Xiao Y.
      • Zhang L.
      • Han L.
      • Dang S.
      • Xu Y.
      • Yang Q.
      • Xu S.
      • Zhu H.
      • Xu Y.
      • Jin Q.
      • Sharma L.
      • Wang L.
      • Wang J.
      Profiling Early Humoral Response to Diagnose Novel Coronavirus Disease(COVID-19).
      ;
      • Jin Y.
      • Wang M.
      • Zuo Z.
      • Fan C.
      • Ye F.
      • Cai Z.
      • Wang Y.
      • Cui H.
      • Pan K.
      • Xu A.
      Diagnostic value and dynamic variance of serum antibody in coronavirus disease 2019.
      ;
      • Pan Y.
      • Zhang D.
      • Yang P.
      • Poon L.L.M.
      • Wang Q.
      Viral load of SARS-CoV-2 in clinical samples.
      ;
      • Padoan A.
      • Cosma C.
      • Sciacovelli L.
      • Faggian D.
      • Plebani M.
      Analytical performances of a chemiluminescence immunoassay for 2019-nCov IgM/IgG and antibody kinetics.
      ;
      • Zhong L.
      • Chuan J.
      • Gong B.O.
      • Shuai P.
      • Zhou Y.
      • Zhang Y.
      • et al.
      Detection of serum IgM and IgG for COVID-19 diagnosis.
      ;
      • Infantino M.
      • Grossi V.
      • Lari B.
      • Bambi R.
      • Perri A.
      • Manneschi M.
      • Terenzi G.
      • Liotti I.
      • Ciotta G.
      • Taddei C.
      • Benucci M.
      • Casprini P.
      • Veneziani F.
      • Fabbri S.
      • Pompetti A.
      • Manfredi M.
      Diagnostic accuracy of an automated chemiluminescentimmunoassay for anti-SARS-CoV-2 IgM and IgG antibodies: an Italian experience.
      ;
      • Xiang F.
      • Wang X.
      • He X.
      • Peng Z.
      • Yang B.
      • Zhang J.
      • Zhou Q.
      • Ye H.
      • Ma Y.
      • Li H.
      • Wei X.
      • Cai P.
      • Ma W.L.
      Antibody Detection and Dynamic Characteristics in Patients with COVID-19.
      ;
      • Long Q.X.
      • Liu B.Z.
      • Deng H.J.
      • Wu G.C.
      • Deng K.
      • Chen Y.K.
      • Liao P.
      • Qiu J.F.
      • Lin Y.
      • Cai X.F.
      • Wang D.Q.
      • Hu Y.
      • Ren J.H.
      • Tang N.
      • Xu Y.Y.
      • Yu L.H.
      • Mo Z.
      • Gong F.
      • Zhang X.L.
      • Tian W.G.
      • Hu L.
      • Zhang X.X.
      • Xiang J.L.
      • Du H.X.
      • Liu H.W.
      • Lang C.H.
      • Luo X.H.
      • Wu S.B.
      • Cui X.P.
      • Zhou Z.
      • Zhu M.M.
      • Wang J.
      • Xue C.J.
      • Li X.F.
      • Wang L.
      • Li Z.J.
      • Wang K.
      • Niu C.C.
      • Yang Q.J.
      • Tang X.J.
      • Zhang Y.
      • Liu X.M.
      • Li J.J.
      • Zhang D.C.
      • Zhang F.
      • Liu P.
      • Yuan J.
      • Li Q.
      • Hu J.L.
      • Chen J.
      • Huang A.L.
      Antibody responses to SARS-CoV-2 in patients with COVID-19.
      ;
      • Perera R.A.
      • Mok C.K.
      • Tsang O.T.
      • Lv H.
      • Ko R.L.
      • Wu N.C.
      • Yuan M.
      • Leung W.S.
      • Chan J.M.
      • Chik T.S.
      • Choi C.Y.
      • Leung K.
      • Chan K.H.
      • Chan K.C.
      • Li K.C.
      • Wu J.T.
      • Wilson I.A.
      • Monto A.S.
      • Poon L.L.
      • Peiris M.
      Serological assays for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), March 2020.
      ;
      • Qu J.
      • Wu C.
      • Li X.
      • Zhang G.
      • Jiang Z.
      • Li X.
      • Zhu Q.
      • Liu L.
      Profile of IgG and IgM antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
      ;
      • Zhao R.
      • Li M.
      • Song H.
      • Chen J.
      • Ren W.
      • Feng Y.
      • Gao G.F.
      • Song J.
      • Peng Y.
      • Su B.
      • Guo X.
      • Wang Y.
      • Chen J.
      • Li J.
      • Sun H.
      • Bai Z.
      • Cao W.
      • Zhu J.
      • Zhang Q.
      • Sun Y.
      • Sun S.
      • Mao X.
      • Su J.
      • Chen X.
      • He A.
      • Gao W.
      • Jin R.
      • Jiang Y.
      • Sun L.
      Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
      ;
      • Cai X.F.
      • Chen J.
      • Hu J.L.
      • Long Q.X.
      • Deng H.J.
      • Fan K.
      • Liao P.
      • Liu B.Z.
      • Wu G.C.
      • Chen Y.K.
      • Li Z.J.
      • Wang K.
      • Zhang X.L.
      • Tian W.G.
      • Xiang J.L.
      • Du H.X.
      • Wang J.
      • Hu Y.
      • Tang N.
      • Lin Y.
      • Ren J.H.
      • Huang L.Y.
      • Wei J.
      • Gan C.Y.
      • Chen Y.M.
      • Gao Q.Z.
      • Chen A.M.
      • He C.L.
      • Wang D.X.
      • Hu P.
      • Zhou F.C.
      • Huang A.L.
      • Liu P.
      • Wang D.Q.
      A Peptide-based Magnetic Chemiluminescence Enzyme Immunoassay for Serological Diagnosis of Coronavirus Disease 2019 (COVID-19).
      ;
      • Hou H.
      • Wang T.
      • Zhang B.
      • Luo Y.
      • Mao L.
      • Wang F.
      • Wu S.
      • Sun Z.
      Detection of IgM and IgG antibodies in patients with coronavirus disease 2019.
      ;
      • Lippi G.
      • Salvagno G.L.
      • Pegoraro M.
      • Militello V.
      • Caloi C.
      • Peretti A.
      • Gaino S.
      • Bassi A.
      • Bovo C.
      • Lo Cascio G.
      Assessment of immune response to SARS-CoV-2 withfully automated MAGLUMI 2019-nCoV IgG and IgM chemiluminescence immunoassays.
      ;
      • Sun B.
      • Feng Y.
      • Mo X.
      • Zheng P.
      • Wang Q.
      • Li P.
      • Peng P.
      • Liu X.
      • Chen Z.
      • Huang H.
      • Zhang F.
      • Luo W.
      • Niu X.
      • Hu P.
      • Wang L.
      • Peng H.
      • Huang Z.
      • Feng L.
      • Li F.
      • Zhang F.
      • Li F.
      • Zhong N.
      • Chen L.
      Kinetics of SARS-CoV-2 specific IgM and IgG responses in COVID-19 patients.
      ;
      • To K.K.
      • Tsang O.T.
      • Leung W.S.
      • Tam A.R.
      • Wu T.C.
      • Lung D.C.
      • et al.
      Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study.
      ;
      • Xie J.
      • Ding C.
      • Li J.
      • Wang Y.
      • Guo H.
      • Lu Z.
      • Wang J.
      • Zheng C.
      • Jin T.
      • Gao Y.
      • He H.
      Characteristics of patients with coronavirus disease (COVID-19) confirmed using an IgM-IgG antibody test.
      ;
      • Bryan A.
      • Pepper G.
      • Wener M.H.
      • Fink S.L.
      • Morishima C.
      • Chaudhary A.
      • Jerome K.R.
      • Mathias P.C.
      • Greninger A.L.
      Performance Characteristics of the Abbott Architect SARS-CoV-2 IgG Assay and Seroprevalence in Boise, Idaho.
      ;
      • Jääskeläinen A.J.
      • Kekäläinen E.
      • Kallio-Kokko H.
      • Mannonen L.
      • Kortela E.
      • Vapalahti O.
      • Kurkela S.
      • Lappalainen M.
      Evaluation of commercial and automated SARS-CoV-2 IgG and IgA ELISAs using coronavirus disease (COVID-19) patient samples.
      ;
      • Montesinos I.
      • Gruson D.
      • Kabamba B.
      • Dahma H.
      • Van den Wijngaert S.
      • Reza S.
      • Carbone V.
      • Vandenberg O.
      • Gulbis B.
      • Wolff F.
      • Rodriguez-Villalobos H.
      Evaluation of two automated and three rapid lateral flow immunoassays for the detection of anti-SARS-CoV-2 antibodies.
      ;
      • Tang M.S.
      • Hock K.G.
      • Logsdon N.M.
      • Hayes J.E.
      • Gronowski A.M.
      • Anderson N.W.
      • Farnsworth C.W.
      Clinical Performance of Two SARS-CoV-2 Serologic Assays.
      ) and 25 pre-print studies (
      • Wang X.
      • Guo X.
      • Xin Q.
      • Chu Y.
      • Li J.
      • Pan Y.
      • Feng Y.
      • Wang Q.
      Neutralizing Antibodies Responses to SARS-CoV-2 in COVID-19 Inpatients and Convalescent Patients.
      ;
      • Lassaunière R.
      • Frische A.
      • Harboe Z.
      • Nielsen A.
      • Fomsgaard A.
      • Krogfelt K.
      • Jørgensen C.
      Evaluation of nine commercial SARS-CoV-2 immunoassays.
      ;
      • Yangchun F.
      Optimize Clinical Laboratory Diagnosis of COVID-19 from Suspect Cases by Likelihood Ratio of SARS-CoV-2 IgM and IgG antibody.
      ;

      Liu R., Liu X., Han H., Shereehn M.A., Niu Z., Li D. et al. The comparative superiority of IgM-IgG antibody test to real-time reverse transcriptase PCR detection for SARS-CoV-2 infection diagnosis 2020 doi: https://doi.org/10.1101/2020.03.28.20045765

      ;
      • Lin D.
      • Liu L.
      • Zhang M.
      • Hu Y.
      • Yang Q.
      • Guo J.
      • Dai Y.
      • Xu Y.
      • Cai Y.
      • Chen X.
      • Huang K.
      • Zhang Z.
      Evaluations of serological test in the diagnosis of 2019 1 novel coronavirus (SARS-CoV-2) infections during the COVID-19 outbreak.
      ;
      • Lou B.
      • Li T.D.
      • Zheng S.F.
      • Su Y.Y.
      • Li Z.Y.
      • Liu W.
      • Yu F.
      • Ge S.X.
      • Zou Q.D.
      • Yuan Q.
      • Lin S.
      • Hong C.M.
      • Yao X.Y.
      • Zhang X.J.
      • Wu D.H.
      • Zhou G.L.
      • Hou W.H.
      • Li T.T.
      • Zhang Y.L.
      • Zhang S.Y.
      • Fan J.
      • Zhang J.
      • Xia N.S.
      • Chen Y.
      Serology characteristics of SARS-CoV-2 infection since the exposure and post symptoms onset.
      ;
      • Liu L.
      • Liu W.
      • Wang S.
      • Zheng S.
      A preliminary study on serological assay for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 238 admitted hospital patients.
      ;
      • Jia X.
      • Zhang P.
      • Tian Y.
      • Wang J.
      • Zeng H.
      • Wang J.
      • Liu J.
      • Chen Z.
      • Zhang L.
      • He H.
      • He K.
      • Liu Y.
      Clinical significance of IgM and IgG test for diagnosis of highly suspected COVID-19 infection.
      ;
      • Zhang J.
      • Liu J.
      • Li N.
      • Liu Y.
      • Ye R.
      • Qin X.
      • Zheng R.
      Serological detection of 2019-nCoV respond to the epidemic: A useful complement to nucleic acid testing.
      ;
      • Xiang J.
      • Yan M.
      • Li H.
      • Liu T.
      • Lin C.
      • Huang S.
      • Shen C.
      Evaluation of Enzyme-Linked Immunoassay and Colloidal Gold-Immunochromatographic Assay Kit for Detection of Novel Coronavirus (SARS-Cov-2) Causing an Outbreak of Pneumonia (COVID-19).
      ;

      Hu Q., Cui X., Liu X., Peng B., Jiang J., Wang X. et al., The production of antibodies for SARS-CoV-2 and its clinical implication 2020 doi: https://doi.org/10.1101/2020.04.20.20065953

      ;

      Ma H., Zeng W., He H., Zhao D., Yang Y., Jiang D., et al., COVID-19 diagnosis and study of serum SARS-CoV-2 specific IgA, IgM and IgG by a quantitative and sensitive immunoassay 2020 doi: https://doi.org/10.1101/2020.04.17.20064907

      ;
      • Qian C.
      • Zhou M.
      • Cheng F.
      • Lin X.
      • Gong Y.
      • Xie X.
      • et al.
      Development and Multicenter Performance Evaluation of The First Fully Automated SARS-CoV-2 IgM and IgG Immunoassays.
      ;

      National COVID Testing Scientific Advisory Panel Evaluation of antibody testing for SARS-Cov-2 using ELISA and lateral flow immunoassay 2020 doi: https://doi.org/10.1101/2020.04.15.20066407

      ;

      Burbelo P.D., Francis X.R., Morishima C., Rawlings S., Smith D., Das S. et al., Detection of Nucleocapsid Antibody to SARS-CoV-2 is More Sensitive than Antibody to Spike Protein in COVID-19 Patients 2020 https://doi.org/10.1101/2020.04.20.20071423

      ;
      • Adams E.R.
      • Augustin Y.
      • Byrne R.L.
      • Clark D.J.
      • Cocozza M.
      • Cubas-Atienzar A.I.
      • et al.
      Rapid development of COVID-19 rapid diagnostics for low resource settings: accelerating delivery through transparency, responsiveness, and open collaboration.
      ;

      Meyer B., Torriani G., Yerly S., Mazza L., Calame A., Arm-Vernez I. et al. Validation of a commercially available SARS-CoV-2 serological Immunoassay medRxiv 2020.05.02.20080879; doi: https://doi.org/10.1101/2020.05.02.20080879

      ;

      Norman M., Gilboa T., Ogata F.A., Maley A.M., Cohen L., Cay Y. et al. Ultra-Sensitive High-Resolution Profiling of Anti-SARS-CoV-2 Antibodies for Detecting Early Seroconversion in COVID-19 Patients medRxiv 2020.04.28.20083691; doi: https://doi.org/10.1101/2020.04.28.20083691

      ;
      • Tuaillon E.
      Detection of SARS-CoV-2 antibodies using commercial assays and seroconversion patterns in hospitalized patients.
      ;
      • Wajnberg A.
      • Mansour M.
      • Leven E.
      • Bouvier N.M.
      • Patel G.
      • Firpo A.
      • et al.
      Humoral immune response and prolonged PCR positivity in a cohort of 1343 SARS-CoV 2 patients in the New York City region.
      ;
      • Wan Y.
      • Li Z.
      • Wank K.
      • Li T.
      • Liao P.
      Performance verification of detecting COVID-19 specific antibody by using four chemiluminescence immunoassay systems.
      ;
      • Xiao T.
      • Wang Y.
      • Yuan J.
      • Ye H.
      • Wei L.
      • Wang H.
      • et al.
      Early viral clearance and antibody kinetics of COVID-19 among asymptomatic carriers.
      ;

      Zhou Q., Zhu D., Yan H., Quan J., Kuang Z., Zhang, W. et al., A preliminary study on analytical performance of serological assay for SARS-CoV-2 IgM/IgG and application in clinical practice medRxiv 2020.05.05.20092551; doi: https://doi.org/10.1101/2020.05.05.20092551

      ;
      • Ozturk T.
      • Howell C.
      • Benameur K.
      • Ramonell R.P.
      • Cashman K.
      Pirmohammed S Cross-sectional IgM and IgG profiles in SARS-CoV-2 infection.
      ;
      • Rosado J.
      • Cockram C.
      • Merkling H.
      • Demeret C.
      • Meola A.
      • Kerneis S.
      Serological signatures of SARS-CoV-2 infection: Implications for antibody-based diagnostics.
      ) reporting on the sensitivity and specificity of immunoassays for COVID-19, with a sample size ranging from 16 to 6001 subjects (Table 1). Most studies were conducted in China, with only a few coming from western countries.
      Overall sensitivity ranged from 0% to 100% and specificity from 78% to 100%, with performance highly time-sensitive, reflecting the dynamics of seroconversion. In general, most assays performed better shortly after initial symptom resolution, accepting the very limited time frames evaluated for all studies to date. In an evaluation of nine commercially available SARS-CoV-2 immunoassays, the sensitivities varied with the duration of disease: early phase, 7–13 days after the onset of disease symptoms (sensitivities 40–86%); middle phase, 14–20 days after the onset of disease symptoms (sensitivities 67–100%); and late phase, ≥21 days after the onset of disease symptoms (sensitivities 78–89%) (
      • Lassaunière R.
      • Frische A.
      • Harboe Z.
      • Nielsen A.
      • Fomsgaard A.
      • Krogfelt K.
      • Jørgensen C.
      Evaluation of nine commercial SARS-CoV-2 immunoassays.
      ).
      The range of assays being released is extensive, with apparently very limited validation. Gonzalez and colleagues reviewed four web databases for SARS-CoV-2 immunoassay, and by 4 April 2020, 226 immunoassays from 20 different countries had already been listed. The technical data sheet was available online for only 22% of the tests, and despite 23 claiming regulatory certification only four had PubMed-listed papers (
      • González J.M.
      • Shelton W.J.
      • Díaz-Vallejo M.
      • Rodriguez-Castellanos V.E.
      • Zuluaga J.D.H.
      • Chamorro D.F.
      • Arroyo-Ariza D.
      Immunological assays for SARS-CoV-2: an analysis of available commercial tests to measure antigen and antibodies.
      ). Despite wide claims for sensitivity and specificity, practically at present it is almost impossible to conclude which antibody test would be the one to use. A pragmatic choice would be to use an automated immunoassay that is scalable, from a well-known established manufacturer, with a complete and clear technical data sheet, which has received regulatory certification issued by the health authority and been independently validated.
      In accordance with this, the most recent novel assays use fully automated chemiluminescence immunoassays implemented on high-throughput laboratory instrumentation. These systems include the MAGLUMI 2000 Plus 2019-nCov IgM and IgG assays (Snibe, China), which has been independently validated in accordance with the Clinical and Laboratory Standards Institute EP15-A3 guideline (
      • Padoan A.
      • Cosma C.
      • Sciacovelli L.
      • Faggian D.
      • Plebani M.
      Analytical performances of a chemiluminescence immunoassay for 2019-nCov IgM/IgG and antibody kinetics.
      ) and the CE-marked Euroimmun, Italy Anti-SARS-CoV-2 IgA and IgG assays, with others, including from Beckman Coulter, Italy for their Access platform and Roche Diagnostics, Italy for their Elecsys platform, under development. However, in independent validation the EUROIMMUN assay exhibited some cross-reactivity in both ELISA with serum samples from the two seasonal CoV patients (HCoV-OC43) who had previously cross-reacted with the MERS-CoV S1 IgG ELISA (
      • Okba N.M.A.
      • Raj V.S.
      • Widjaja I.
      • GeurtsvanKessel C.H.
      • de Bruin E.
      • Chandler F.D.
      • et al.
      Sensitive and Specific Detection of Low-Level Antibody Responses in Mild Middle East Respiratory Syndrome Coronavirus Infections.
      ). On comparison of their respective performances for 131 known cases, there was concordance for the IgG assays of only 88% (kappa statistic 0.47; 95% confidence interval [CI] 0.26–0.68). Despite involving different immunoglobulin classes, an analogous analysis between MAGLUMI 2019-nCoV IgM positive/negative and EUROIMMUN Anti-SARS-CoV-2 IgA positive/negative results yielded an overall concordance of 90% (kappa statistic 0.39; 95% CI 0.14–0.65). The IgG assays also exhibited different concordance during the early phases of symptom onset, with concordance improving 10–21 days after symptom onset. Further studies with longer timelines and known cases with a range of symptoms will help confirm the alignment of these assays. Inevitably, it is anticipated that there will be an enormous number of studies comparing the available assays, with the advantages and disadvantages of the respective assays being discussed at length.

      Rapid serological tests

      POC immunoassays have also been developed for the rapid detection of SARS-CoV-2 antibodies (IgG and IgM). The primary advantage of these tests, as with a home pregnancy test, is being able to obtain a diagnosis without sending samples to centralized laboratories. This enables communities without the necessary laboratory infrastructure to detect SARS-CoV-2-exposed subjects using only finger prick testing rather than formal blood draws, thereby reducing training requirements and allowing clinicians to have a validated test at the bedside. As these devices are cheap to manufacture, store and distribute, and provided that a positive antibody test were confirmed to be an accurate surrogate for immunity to infection, they would also be able inform decision making. This would particularly be the case as secure confirmation of antibody status would reduce anxiety, provide confidence to allow individuals to relax social distancing measures, and guide policy makers in the staged release of population lockdown, potentially in tandem with digital approaches to contact tracing.
      The rapid POC immunoassays are generally LFIA (
      • Li Z.
      • Yi Y.
      • Luo X.
      • Xiong N.
      • Liu Y.
      • Li S.
      • Sun R.
      • Wang Y.
      • Hu B.
      • Chen W.
      • Zhang Y.
      • Wang J.
      • Huang B.
      • Lin Y.
      • Yang J.
      • Cai W.
      • Wang X.
      • Cheng J.
      • Chen Z.
      • Sun K.
      • Pan W.
      • Zhan Z.
      • Chen L.
      • Ye F.
      Development and Clinical Application of A Rapid IgM-IgG Combined Antibody Test for SARS-CoV-2 Infection Diagnosis.
      ). In lateral flow assays, a membrane strip is coated with two lines: gold nanoparticle–antibody conjugates are located on one line and bind antibodies on the other. The blood sample from the patient is put on the membrane, and the proteins are drawn through the membrane strip by capillary action. As it passes the first line, the antigen binds to the gold nanoparticle–antibody conjugate, and the complex flows across the membrane. Generally, rapid assays have a low diagnostic performance compared with ELISA assays, which is explained not only by the well-known technical differences between the two methodologies, but also by possible low antibody concentrations that may further contribute to the false-negative results observed with the rapid tests.
      At present, 12 peer-reviewed articles (
      • Li Z.
      • Yi Y.
      • Luo X.
      • Xiong N.
      • Liu Y.
      • Li S.
      • Sun R.
      • Wang Y.
      • Hu B.
      • Chen W.
      • Zhang Y.
      • Wang J.
      • Huang B.
      • Lin Y.
      • Yang J.
      • Cai W.
      • Wang X.
      • Cheng J.
      • Chen Z.
      • Sun K.
      • Pan W.
      • Zhan Z.
      • Chen L.
      • Ye F.
      Development and Clinical Application of A Rapid IgM-IgG Combined Antibody Test for SARS-CoV-2 Infection Diagnosis.
      ;
      • Cassaniti I.
      • Novazzi F.
      • Giardina F.
      • Salinaro F.
      • Sachs M.
      • Perlini S.
      • Bruno R.
      • Mojoli F.
      • Baldanti F.
      Members of the San Matteo Pavia COVID-19 Task Force
      Performance of VivaDiag COVID-19 IgM/IgG Rapid Test is inadequate for diagnosis of COVID-19 in acute patients referring to emergency room department.
      ;
      • Lee Y.L.
      • Liao C.H.
      • Liu P.Y.
      • Cheng C.Y.
      • Chung M.Y.
      • Liu C.E.
      • Chang S.Y.
      • Hsueh P.R.
      Dynamics of anti-SARS-Cov-2 IgM and IgG antibodies among COVID-19 patients.
      ;
      • Shen B.
      • Zheng Y.
      • Zhang X.
      • Zhang W.
      • Wang D.
      • Jin J.
      • Lin R.
      • Zhang Y.
      • Zhu G.
      • Zhu H.
      • Li J.
      • Xu J.
      • Ding X.
      • Chen S.
      • Lu R.
      • He Z.
      • Zhao H.
      • Ying L.
      • Zhang C.
      • Lv D.
      • Chen B.
      • Chen J.
      • Zhu J.
      • Hu B.
      • Hong C.
      • Xu X.
      • Chen J.
      • Liu C.
      • Zhou K.
      • Li J.
      • Zhao G.
      • Shen W.
      • Chen C.
      • Shao C.
      • Shen X.
      • Song J.
      • Wang Z.
      • Meng Y.
      • Wang C.
      • Han J.
      • Chen A.
      • Lu D.
      • Qian B.
      • Chen H.
      • Gao H.
      Clinical evaluation of a rapid colloidal gold immunochromatography assay for SARS-Cov-2 IgM/IgG.
      ;
      • Döhla M.
      • Boesecke C.
      • Schulte B.
      • Diegmann C.
      • Sib E.
      • Richter E.
      • Eschbach-Bludau M.
      • Aldabbagh S.
      • Marx B.
      • Eis-Hübinger A.M.
      • Schmithausen R.M.
      • Streeck H.
      Rapid point-of-care testing for SARS-CoV-2 in a community screening setting shows low sensitivity.
      ;
      • Hoffman T.
      • Nissen K.
      • Krambrich J.
      • Rönnberg B.
      • Akaberi D.
      • Esmaeilzadeh M.
      • Salaneck E.
      • Lindahl J.
      • Lundkvist Å.
      Evaluation of a COVID-19 IgM and IgG rapid test; an efficient tool for assessment of past exposure to SARS-CoV-2.
      ;
      • Imai K.
      • Tabata S.
      • Ikeda M.
      • Noguchi S.
      • Kitagawa Y.
      • Matuoka M.
      • Miyoshi K.
      • Tarumoto N.
      • Sakai J.
      • Ito T.
      • Maesaki S.
      • Tamura K.
      • Maeda T.
      Clinical evaluation of an immunochromatographic IgM/IgG antibody assay and chest computed tomography for the diagnosis of COVID-19.
      ;
      • Pan Y.
      • Li X.
      • Yang G.
      • Fan J.
      • Tang Y.
      • Zhao J.
      • Long X.
      • Guo S.
      • Zhao Z.
      • Liu Y.
      • Hu H.
      • Xue H.
      • Li Y.
      Serological immunochromatographic approach in diagnosis with SARS-CoV-2 infected COVID-19 patients.
      ;
      • Spicuzza L.
      • Montineri A.
      • Manuele R.
      • Crimi C.
      • Pistorio M.P.
      • Campisi R.
      • Vancheri C.
      • Crimi N.
      Reliability and usefulness of a rapid IgM-IgG antibody test for the diagnosis of SARS-CoV-2 infection: A preliminary report.
      ;
      • Yong G.
      • Yi Y.
      • Tuantuan L.
      • Xiaowu L.
      • Xiuyong L.
      • Ang L.
      • Mingfeng H.
      Evaluation of the auxiliary diagnosis value of antibodies assays for the detection of novel coronavirus (SARS-Cov-2).
      ;
      • Demey B.
      • Daher N.
      • François C.
      • Lanoix J.P.
      • Duverlie G.
      • Castelain S.
      • Brochot E.
      Dynamic profile for the detection of anti-SARS-CoV-2 antibodies using four immunochromatographic assays.
      ;
      • Montesinos I.
      • Gruson D.
      • Kabamba B.
      • Dahma H.
      • Van den Wijngaert S.
      • Reza S.
      • Carbone V.
      • Vandenberg O.
      • Gulbis B.
      • Wolff F.
      • Rodriguez-Villalobos H.
      Evaluation of two automated and three rapid lateral flow immunoassays for the detection of anti-SARS-CoV-2 antibodies.
      ) and 9 pre-print studies (
      • Garcia F.P.
      • Tanoira P.
      • Romanyk Cabrera J.P.
      • Serrano T.
      • Herruz P.G.
      • Gonzalez J.C.
      Rapid diagnosis of SARS-CoV-2 infection by detecting IgG and IgM antibodies with an immunochromatographic device: a prospective single-center study.
      ;
      • Lassaunière R.
      • Frische A.
      • Harboe Z.
      • Nielsen A.
      • Fomsgaard A.
      • Krogfelt K.
      • Jørgensen C.
      Evaluation of nine commercial SARS-CoV-2 immunoassays.
      ;
      • Liu Y.
      • Liu Y.
      • Diao B.
      • Ren F.
      • Wang Y.
      • Ding J.
      • Huang O.
      Diagnostic Indexes of a Rapid IgG/IgM Combined Antibody Test for SARS-CoV-2.
      ;
      • Yong G.
      • Yi Y.
      • Tuantuan L.
      • Xiaowu L.
      • Xiuyong L.
      • Ang L.
      • Mingfeng H.
      Evaluation of the auxiliary diagnosis value of antibodies assays for the detection of novel coronavirus (SARS-Cov-2).
      ;
      • Lou B.
      • Li T.D.
      • Zheng S.F.
      • Su Y.Y.
      • Li Z.Y.
      • Liu W.
      • Yu F.
      • Ge S.X.
      • Zou Q.D.
      • Yuan Q.
      • Lin S.
      • Hong C.M.
      • Yao X.Y.
      • Zhang X.J.
      • Wu D.H.
      • Zhou G.L.
      • Hou W.H.
      • Li T.T.
      • Zhang Y.L.
      • Zhang S.Y.
      • Fan J.
      • Zhang J.
      • Xia N.S.
      • Chen Y.
      Serology characteristics of SARS-CoV-2 infection since the exposure and post symptoms onset.
      ;
      • Bendavid E.
      • Mulaney B.
      • Sood N.
      • Shah S.
      • Ling E.
      • Bromley-Dulfano R.
      • et al.
      COVID-19 Antibody Seroprevalence in Santa Clara County, California.
      ;
      • Paradiso A.V.
      • De Summa S.
      • Loconsole D.
      • Procacci V.
      • Sallustio A.
      • Centrone F.
      • Silvestris N.
      • Cafagna V.
      • De Palma G.
      • Tufaro A.
      • Garrisi V.
      • Chironna M.
      Clinical meanings of rapid serological assay in patients tested for SARS-Co2 RT-PCR.
      ; National COVID testing Scientific Advisory Board, 2020;
      • Tuaillon E.
      Detection of SARS-CoV-2 antibodies using commercial assays and seroconversion patterns in hospitalized patients.
      ) have reported on the diagnostic performance of rapid assays (summarized in Table 1).
      In the published studies, sensitivity and specificity ranged from 9% to 88.6% and from 88.9% to 91.7%, respectively (Table 1), while in the pre-print articles sensitivity and specificity ranged from 30% to 98.8% and from 89% to 100%, respectively. Of note the sensitivity of these tests performed in countries other than China were substantially lower than those reported for studies conducted in China. Extensive evaluation of manufacturers’ claims related to the performance of these tests and optimal timing will be required before they are suitable for widespread routine clinical use. For example, the performance of the VivaDiag, VivaCheck Biotech, China COVID-19 IgM/IgG Rapid Test was evaluated in 30 cases 7 days after confirmed NAAT testing, and despite this five (16.7%) cases were negative for both IgG and IgM (
      • Cassaniti I.
      • Novazzi F.
      • Giardina F.
      • Salinaro F.
      • Sachs M.
      • Perlini S.
      • Bruno R.
      • Mojoli F.
      • Baldanti F.
      Members of the San Matteo Pavia COVID-19 Task Force
      Performance of VivaDiag COVID-19 IgM/IgG Rapid Test is inadequate for diagnosis of COVID-19 in acute patients referring to emergency room department.
      ). Furthermore, when evaluating 50 patients with acute illness presenting in the emergency room, of whom 38 were positive on RT-PCR, the sensitivity of the VivaDiag COVID-19 IgM/IgG Rapid Test was only 18.4%, its specificity was 91.7%, while the NPV was 26.2% and the PPV was 87.5% (
      • Cassaniti I.
      • Novazzi F.
      • Giardina F.
      • Salinaro F.
      • Sachs M.
      • Perlini S.
      • Bruno R.
      • Mojoli F.
      • Baldanti F.
      Members of the San Matteo Pavia COVID-19 Task Force
      Performance of VivaDiag COVID-19 IgM/IgG Rapid Test is inadequate for diagnosis of COVID-19 in acute patients referring to emergency room department.
      ). The same VivaDiag test was evaluated in 525 healthcare workers in Italy, with only six testing positive; none was positive by NAAT testing or symptomatic, and only three had a confirmed positive result on the MAGLUMI chemiluminescence IgG assay (
      • Paradiso A.V.
      • De Summa S.
      • Silvestris N.
      • Tommasi S.
      • Tufaro A.
      • De Palma G.
      • Larocca A.M.V.
      • Chironna M.
      • D'Addabbo V.
      • Raffaele D.
      • Cafagna V.
      • Garrisi V.
      Rapid serological tests have a role in asymptomatic health workers COVID-19 screening.
      ). Evaluation of six POC tests in a mix of 111 patients with COVID-19, other CoV or other viruses and negative controls revealed sensitivities ranging from 83% to 93% and NPV of 74–92% (
      • Lassaunière R.
      • Frische A.
      • Harboe Z.
      • Nielsen A.
      • Fomsgaard A.
      • Krogfelt K.
      • Jørgensen C.
      Evaluation of nine commercial SARS-CoV-2 immunoassays.
      ). In keeping with other studies, the diagnostic performance of these tests reflected the duration of the illness, with the worst performance observed in the first 2 weeks after symptom onset (
      • Lassaunière R.
      • Frische A.
      • Harboe Z.
      • Nielsen A.
      • Fomsgaard A.
      • Krogfelt K.
      • Jørgensen C.
      Evaluation of nine commercial SARS-CoV-2 immunoassays.
      ). Finally, formal evaluation of nine commercially available LFIA in a case-control mix of 182 samples revealed sensitives of 55–70% (

      Ma H., Zeng W., He H., Zhao D., Yang Y., Jiang D., et al., COVID-19 diagnosis and study of serum SARS-CoV-2 specific IgA, IgM and IgG by a quantitative and sensitive immunoassay 2020 doi: https://doi.org/10.1101/2020.04.17.20064907

      ).
      For all studies to date, sample size has been limited, and further testing across a large diverse population from a range of geographical locations and ethnic groups is required, with inclusion of children and individuals with autoimmune disease and immunosuppression. With extensive evaluation, it is likely that technical performance may deteriorate. At present, evaluation of the current LFIA devices suggest that although they may provide some information for population-level surveys, their performance is inadequate for most individual patient applications.

      Clinical interpretation of the COVID-19 tests

      The interpretation of a test for SARS-CoV-2 will depend on a combination of the accuracy of the test and the estimated risk of COVID-19 prior to performing the test (
      • Watson J.
      • Whiting P.F.
      • Brush J.e.
      Interpreting a Covid-19 test results.
      ). A positive direct antigen test and specifically NAAT is strongly suggestive of current infection due to its high specificity but moderate sensitivity, and the patient can be reassured that the clinician is confident that they have COVID-19 and should be managed in accordance with local policies regarding positive cases. In contrast, negative tests need to be interpreted with caution, and a single negative SARS-CoV-2 test in a patient with strongly suggestive symptoms should not be relied upon to exclude COVID-19. In this situation, it would still be safer for the patient to be treated as a positive case, and local policies regarding re-testing and isolation to be followed. For the serological tests, the clinical implication of seroconversion with respect to future immunity continues to be elucidated, but similar principles for evaluating the test result in the clinical context and history of previous infection or exposure is critical, particularly as a false-positive result could lead to false reassurance and inappropriate behaviour that might enhance community disease transmission.

      Conclusions

      At present, NAAT based methodologies remain the cornerstone of in-vitro diagnostic assays for SARS-CoV-2. There is an urgent need for the development of serological assays with high sensitivity for screening and adequate specificity to avoid unnecessary interventions, and confirmation that seropositivity equates to immunity. At present, none of the POC diagnostic tests for SARS-CoV-2 appears suitable for wide-scale deployment, and large prospective studies are urgently needed to clarify their utility. Evaluation of the performance of the potentially scalable high-throughput immunoassays is ongoing, but extensive validation across different populations will be required before they can be routinely used to inform critical decision making for clinicians, the public health community and policy makers.

      Acknowledgements

      This work was supported by the National Institute for Health Research Biomedical Centre at the University Hospitals Bristol NHS Foundation Trust and the University of Bristol (SMN). The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the National Institute for Health Research or the Department of Health and Social Care, or any other funders mentioned here.

      Declaration

      ALM has participated in Advisory Boards and received speaker's and consultancy fees from Beckman Coulter, Gedeon Richeter, Ferring, IBSA, Merck, MSD, Roche Diagnostics and Theramex. SMN has participated in Advisory Boards and received speaker's and consultancy fees from Access Fertility, Beckman Coulter, Ferring, Finox, Merck, MSD, Roche Diagnostics and The Fertility Partnership. The other authors report no financial or commercial conflicts of interest.

      References

        • Adams E.R.
        • Augustin Y.
        • Byrne R.L.
        • Clark D.J.
        • Cocozza M.
        • Cubas-Atienzar A.I.
        • et al.
        Rapid development of COVID-19 rapid diagnostics for low resource settings: accelerating delivery through transparency, responsiveness, and open collaboration.
        medRxiv. 2020; (.04.29.20082099https://doi.org/)https://doi.org/10.1101/2020.04.29.20082099
        • Bendavid E.
        • Mulaney B.
        • Sood N.
        • Shah S.
        • Ling E.
        • Bromley-Dulfano R.
        • et al.
        COVID-19 Antibody Seroprevalence in Santa Clara County, California.
        medRxiv. 2020; (04.14.20062463https://doi.org/)https://doi.org/10.1101/2020.04.14.20062463
        • Bryan A.
        • Pepper G.
        • Wener M.H.
        • Fink S.L.
        • Morishima C.
        • Chaudhary A.
        • Jerome K.R.
        • Mathias P.C.
        • Greninger A.L.
        Performance Characteristics of the Abbott Architect SARS-CoV-2 IgG Assay and Seroprevalence in Boise, Idaho.
        J. Clin. Microbiol. 2020; (May 7pii: JCM.00941-20)https://doi.org/10.1128/JCM.00941-20
        • Brenner H.
        • Gefeller O.
        Variation of sensitivity, specificity, likelihood ratios and predictive values with disease prevalence.
        Statistics in medicine. 1997; 16: 981-991
      1. Burbelo P.D., Francis X.R., Morishima C., Rawlings S., Smith D., Das S. et al., Detection of Nucleocapsid Antibody to SARS-CoV-2 is More Sensitive than Antibody to Spike Protein in COVID-19 Patients 2020 https://doi.org/10.1101/2020.04.20.20071423

        • Cai X.F.
        • Chen J.
        • Hu J.L.
        • Long Q.X.
        • Deng H.J.
        • Fan K.
        • Liao P.
        • Liu B.Z.
        • Wu G.C.
        • Chen Y.K.
        • Li Z.J.
        • Wang K.
        • Zhang X.L.
        • Tian W.G.
        • Xiang J.L.
        • Du H.X.
        • Wang J.
        • Hu Y.
        • Tang N.
        • Lin Y.
        • Ren J.H.
        • Huang L.Y.
        • Wei J.
        • Gan C.Y.
        • Chen Y.M.
        • Gao Q.Z.
        • Chen A.M.
        • He C.L.
        • Wang D.X.
        • Hu P.
        • Zhou F.C.
        • Huang A.L.
        • Liu P.
        • Wang D.Q.
        A Peptide-based Magnetic Chemiluminescence Enzyme Immunoassay for Serological Diagnosis of Coronavirus Disease 2019 (COVID-19).
        J. Infect. Dis. 2020; (May 8pii: jiaa243)https://doi.org/10.1093/infdis/jiaa243
        • Cassaniti I.
        • Novazzi F.
        • Giardina F.
        • Salinaro F.
        • Sachs M.
        • Perlini S.
        • Bruno R.
        • Mojoli F.
        • Baldanti F.
        • Members of the San Matteo Pavia COVID-19 Task Force
        Performance of VivaDiag COVID-19 IgM/IgG Rapid Test is inadequate for diagnosis of COVID-19 in acute patients referring to emergency room department.
        J. Med. Virol. 2020; https://doi.org/10.1002/jmv.25800
        • Che X.Y.
        • Qiu L.W.
        • Pan Y.X.
        • Wen K.
        • Hao W.
        • Zhang L.Y.
        • Wang Y.D.i.
        • Liao Z.Y.
        • Hua X.
        • Cheng V.C.C.
        • Yuen K.Y.
        Sensitive and Specific Monoclonal Antibody-Based Capture Enzyme Immunoassay for Detection of Nucleocapsid Antigen in Sera from Patients with Severe Acute Respiratory Syndrome.
        J. Clin. Microbiol. 2004; 42 (https://doi.org/): 2629-2635https://doi.org/10.1128/JCM.42.6.2629-2635.2004
        • Chen Y.
        • Liu Q.
        • Guo D.
        Emerging coronaviruses: Genome structure, replication, and pathogenesis.
        J. Med. Virol. 2020; 92: 418-423
        • Chen W.
        • Lan Y.
        • Yuan X.
        • Deng X.
        • Li Y.
        • Cai X.
        • Li L.
        • He R.
        • Tan Y.
        • Deng X.
        • Gao M.
        • Tang G.
        • Zhao L.
        • Wang J.
        • Fan Q.
        • Wen C.
        • Tong Y.
        • Tang Y.
        • Hu F.
        • Li F.
        • Tang X.
        Detectable 2019-CoV viral RNA in blood is a strong indicator for the further clinical severity.
        Emerg. Microbes. Infect. 2020; 9: 469-473
        • Choe P.G.
        • Perera R.A.P.M.
        • Park W.B.
        • Song K.H.
        • Bang J.H.
        • Kim E.S.
        • et al.
        MERS-CoV Antibody Responses 1 Year after Symptom Onset, South Korea, 2015.
        Emerg. Infect. Dis. 2017; 23: 1079-1084
      2. Comar M., Brumat M., Concas M.P., Argentini G., Bianco A., Bicego L. et al. COVID-19 experience: first Italian survey on healthcare staff members from a Mother-Child Research hospital using combined molecular and rapid immunoassays test 2020 doi: https://doi.org/10.1101/2020.04.19.20071563

        • Corman V.M.
        • Landt O.
        • Kaiser M.
        • Molenkamp R.
        • Meijer A.
        • Chu D.K.
        • et al.
        Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR.
        Euro Surveill. 2020; https://doi.org/10.2807/1560-7917.ES.2020.25.3.2000045
        • Demey B.
        • Daher N.
        • François C.
        • Lanoix J.P.
        • Duverlie G.
        • Castelain S.
        • Brochot E.
        Dynamic profile for the detection of anti-SARS-CoV-2 antibodies using four immunochromatographic assays.
        J Infect. 2020; (May 7. pii: S0163-4453(20)30244-9)https://doi.org/10.1016/j.jinf.2020.04.033
        • Di B.
        • Hao W.
        • Gao Y.
        • Wang M.
        • Wang Y.
        • Di Q.i.u.
        • et al.
        Monoclonal Antibody-Based Antigen Capture Enzyme-Linked Immunosorbent Assay Reveals High Sensitivity of the Nucleocapsid Protein in Acute-Phase Sera of Severe Acute Respiratory Syndrome Patients.
        Clin. Diagn. Lab. Immunol. 2005; 12 (https://doi.org/): 135-140https://doi.org/10.1128/CDLI.12.1.135-140.2005
        • Diao B.
        • Wen K.
        • Chen J.
        • Liu Y.
        • Yuan Z.
        • Han C.
        • Chen J.
        • Pan Y.
        • Chen L.
        • Dan Y.
        • Wang J.
        • Chen Y.
        • Deng G.
        • Zhou H.
        • Wu Y.
        Diagnosis of Acute Respiratory Syndrome Coronavirus 2 Infection by Detection of Nucleocapsid Protein.
        medRxiv. 2020; (03.07.20032524doi: https://doi.org/)https://doi.org/10.1101/2020.03.07.20032524
        • Döhla M.
        • Boesecke C.
        • Schulte B.
        • Diegmann C.
        • Sib E.
        • Richter E.
        • Eschbach-Bludau M.
        • Aldabbagh S.
        • Marx B.
        • Eis-Hübinger A.M.
        • Schmithausen R.M.
        • Streeck H.
        Rapid point-of-care testing for SARS-CoV-2 in a community screening setting shows low sensitivity.
        Public Health. 2020; 182: 170-172
        • Doi A.
        • Iwata K.
        • Kuroda H.
        • Hasuike T.
        • Nasu S.
        • Kanda A.
        • Nagao T.
        • Nishioka H.
        • Tomii K.
        • Morimoto T.
        • Kihara Y.
        Estimation of seroprevalence of novel coronavirus disease (COVID-19) using preserved serum at an outpatient setting in Kobe, Japan: A cross-sectional study.
        medRxiv. 2020; (04.26.20079822doi: https://doi.org/)https://doi.org/10.1101/2020.04.26.20079822
        • Du Z.
        • Zhu F.
        • Guo F.
        • Yang B.
        • Wang T.
        Detection of antibodies against SARS-CoV-2in patients with COVID-19.
        J. Med. Virol. 2020; (Apr)https://doi.org/10.1002/jmv.25820
        • Erikstrup C.
        • Hother C.E.
        • Pdersen O.B.V.
        • Molbak K.
        • Skov R.L.
        • Holm D.K.
        • et al.
        Estimation of SARS-CoV-2 infection fatality rate by real-time antibody screening of blood donors.
        medRxiv. 2020; (04.24.20075291doi: https://doi.org/)https://doi.org/10.1101/2020.04.24.20075291
        • Garcia F.P.
        • Tanoira P.
        • Romanyk Cabrera J.P.
        • Serrano T.
        • Herruz P.G.
        • Gonzalez J.C.
        Rapid diagnosis of SARS-CoV-2 infection by detecting IgG and IgM antibodies with an immunochromatographic device: a prospective single-center study.
        MedRxiv. 2020; (doi.org/)https://doi.org/10.1101/2020.04.11.20062158
        • González J.M.
        • Shelton W.J.
        • Díaz-Vallejo M.
        • Rodriguez-Castellanos V.E.
        • Zuluaga J.D.H.
        • Chamorro D.F.
        • Arroyo-Ariza D.
        Immunological assays for SARS-CoV-2: an analysis of available commercial tests to measure antigen and antibodies.
        MedRxiv. 2020; (https://doi.org/)https://doi.org/10.1101/2020.03.17.20037713
        • Grzelak L.
        • Temmam S.
        • Planchais C.
        • Demeret C.
        • Huon C.
        • Guivel F.
        • et al.
        SARS-CoV-2 serological analysis of COVID-19 hospitalized patients, pauci-symptomatic individuals and blood donors.
        medRxiv. 2020; (04.21.20068858doi: https://doi.org/)https://doi.org/10.1101/2020.04.21.20068858
        • Guan W.J.
        • Ni Z.Y.
        • Hu Y.
        • Liang W.H.
        • Ou C.Q.
        • He J.X.
        • et al.
        Clinical Characteristics of Coronavirus Disease 2019 in China.
        N. Engl. J. Med. 2020; https://doi.org/10.1056/NEJMoa2002032
        • Guo L.
        • Ren L.
        • Yang S.
        • Xiao M.
        • Chang
        • Yang F.
        • Dela Cruz C.S.
        • Wang Y.
        • Wu C.
        • Xiao Y.
        • Zhang L.
        • Han L.
        • Dang S.
        • Xu Y.
        • Yang Q.
        • Xu S.
        • Zhu H.
        • Xu Y.
        • Jin Q.
        • Sharma L.
        • Wang L.
        • Wang J.
        Profiling Early Humoral Response to Diagnose Novel Coronavirus Disease(COVID-19).
        Clin. Infect. Dis. 2020; https://doi.org/10.1093/cid/ciaa310
        • He X.
        • Lau E.H.Y.
        • Wu P.
        • Deng X.
        • Wang J.
        • Hao X.
        • et al.
        Temporal dynamics in viral shedding and transmissibility of COVID-19.
        Nat. Med. 2020; https://doi.org/10.1038/s41591-020-0869-5
        • Hoffman T.
        • Nissen K.
        • Krambrich J.
        • Rönnberg B.
        • Akaberi D.
        • Esmaeilzadeh M.
        • Salaneck E.
        • Lindahl J.
        • Lundkvist Å.
        Evaluation of a COVID-19 IgM and IgG rapid test; an efficient tool for assessment of past exposure to SARS-CoV-2.
        Infect. Ecol. Epidemiol. 2020; 101754538
        • Hou H.
        • Wang T.
        • Zhang B.
        • Luo Y.
        • Mao L.
        • Wang F.
        • Wu S.
        • Sun Z.
        Detection of IgM and IgG antibodies in patients with coronavirus disease 2019.
        Clin. Transl. Immunology. 2020; 9 (May 6): e01136https://doi.org/10.1002/cti2.1136
      3. Hu Q., Cui X., Liu X., Peng B., Jiang J., Wang X. et al., The production of antibodies for SARS-CoV-2 and its clinical implication 2020 doi: https://doi.org/10.1101/2020.04.20.20065953

        • Huang X.
        • Wei F.
        • Hu L.
        • Wen L.
        • Chen K.
        Epidemiology and Clinical Characteristics of COVID-19.
        Arch. Iran. Med. 2020; 23: 268-271https://doi.org/10.34172/aim.2020.09
        • Imai K.
        • Tabata S.
        • Ikeda M.
        • Noguchi S.
        • Kitagawa Y.
        • Matuoka M.
        • Miyoshi K.
        • Tarumoto N.
        • Sakai J.
        • Ito T.
        • Maesaki S.
        • Tamura K.
        • Maeda T.
        Clinical evaluation of an immunochromatographic IgM/IgG antibody assay and chest computed tomography for the diagnosis of COVID-19.
        J. Clin. Virol. 2020; 128104393https://doi.org/10.1016/j.jcv.2020.104393
        • Infantino M.
        • Grossi V.
        • Lari B.
        • Bambi R.
        • Perri A.
        • Manneschi M.
        • Terenzi G.
        • Liotti I.
        • Ciotta G.
        • Taddei C.
        • Benucci M.
        • Casprini P.
        • Veneziani F.
        • Fabbri S.
        • Pompetti A.
        • Manfredi M.
        Diagnostic accuracy of an automated chemiluminescentimmunoassay for anti-SARS-CoV-2 IgM and IgG antibodies: an Italian experience.
        J. Med. Virol. 2020; https://doi.org/10.1002/jmv.25932
        • Jääskeläinen A.J.
        • Kekäläinen E.
        • Kallio-Kokko H.
        • Mannonen L.
        • Kortela E.
        • Vapalahti O.
        • Kurkela S.
        • Lappalainen M.
        Evaluation of commercial and automated SARS-CoV-2 IgG and IgA ELISAs using coronavirus disease (COVID-19) patient samples.
        Euro. Surveill. 2020 May; 25https://doi.org/10.2807/1560-7917.ES.2020.25.18.2000603
        • Jia X.
        • Zhang P.
        • Tian Y.
        • Wang J.
        • Zeng H.
        • Wang J.
        • Liu J.
        • Chen Z.
        • Zhang L.
        • He H.
        • He K.
        • Liu Y.
        Clinical significance of IgM and IgG test for diagnosis of highly suspected COVID-19 infection.
        medRxiv. 2020; (02.28.20029025doi: https://doi.org/)https://doi.org/10.1101/2020.02.28.20029025
        • Jin Y.
        • Wang M.
        • Zuo Z.
        • Fan C.
        • Ye F.
        • Cai Z.
        • Wang Y.
        • Cui H.
        • Pan K.
        • Xu A.
        Diagnostic value and dynamic variance of serum antibody in coronavirus disease 2019.
        Int. J. Infect. Dis. 2020; 94: 49-52https://doi.org/10.1016/j.ijid.2020.03.065
        • Korth J.
        • Wilde B.
        • Dolff S.
        • Anastasiou O.E.
        • Krawczyk A.
        • Jahn M.
        • Cordes S.
        • Ross B.
        • Esser S.
        • Lindemann M.
        • Kribben A.
        • Dittmer U.
        • Witzke O.
        • Herrmann A.
        SARS-CoV-2-specific antibody detection in healthcare workers in Germany with direct contact to COVID-19 patients.
        J. Clin. Virol. 2020; (May 13)104437https://doi.org/10.1016/j.jcv.2020.104437
        • Lassaunière R.
        • Frische A.
        • Harboe Z.
        • Nielsen A.
        • Fomsgaard A.
        • Krogfelt K.
        • Jørgensen C.
        Evaluation of nine commercial SARS-CoV-2 immunoassays.
        medRxiv. 2020; https://doi.org/10.1101/2020.04.09.20056325
        • Lee Y.L.
        • Liao C.H.
        • Liu P.Y.
        • Cheng C.Y.
        • Chung M.Y.
        • Liu C.E.
        • Chang S.Y.
        • Hsueh P.R.
        Dynamics of anti-SARS-Cov-2 IgM and IgG antibodies among COVID-19 patients.
        J. Infect. 2020; (Apr 23pii: S0163-4453(20)30230-9. doi: 0.1016/j.jinf.2020.04.019)
        • Li Z.
        • Yi Y.
        • Luo X.
        • Xiong N.
        • Liu Y.
        • Li S.
        • Sun R.
        • Wang Y.
        • Hu B.
        • Chen W.
        • Zhang Y.
        • Wang J.
        • Huang B.
        • Lin Y.
        • Yang J.
        • Cai W.
        • Wang X.
        • Cheng J.
        • Chen Z.
        • Sun K.
        • Pan W.
        • Zhan Z.
        • Chen L.
        • Ye F.
        Development and Clinical Application of A Rapid IgM-IgG Combined Antibody Test for SARS-CoV-2 Infection Diagnosis.
        J. Med. Virol. 2020; 27: 25727
        • Lin D.
        • Liu L.
        • Zhang M.
        • Hu Y.
        • Yang Q.
        • Guo J.
        • Dai Y.
        • Xu Y.
        • Cai Y.
        • Chen X.
        • Huang K.
        • Zhang Z.
        Evaluations of serological test in the diagnosis of 2019 1 novel coronavirus (SARS-CoV-2) infections during the COVID-19 outbreak.
        medRxiv. 2020; (03.27.20045153; doi: https://doi.org/)https://doi.org/10.1101/2020.03.27.20045153
        • Lippi G.
        • Salvagno G.L.
        • Pegoraro M.
        • Militello V.
        • Caloi C.
        • Peretti A.
        • Gaino S.
        • Bassi A.
        • Bovo C.
        • Lo Cascio G.
        Assessment of immune response to SARS-CoV-2 withfully automated MAGLUMI 2019-nCoV IgG and IgM chemiluminescence immunoassays.
        Clin. Chem. Lab. Med. 2020; (Apr 16.pii:/j/cclm.ahead-of-print/cclm-2020-0473/cclm-2020-0473.xml.)https://doi.org/10.1515/cclm-2020-0473
        • Liu L.
        • Liu W.
        • Wang S.
        • Zheng S.
        A preliminary study on serological assay for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 238 admitted hospital patients.
        medRxiv. 2020; (03.06.20031856; doi: https://doi.org/)https://doi.org/10.1101/2020.03.06.20031856
      4. Liu R., Liu X., Han H., Shereehn M.A., Niu Z., Li D. et al. The comparative superiority of IgM-IgG antibody test to real-time reverse transcriptase PCR detection for SARS-CoV-2 infection diagnosis 2020 doi: https://doi.org/10.1101/2020.03.28.20045765

        • Liu Y.
        • Liu Y.
        • Diao B.
        • Ren F.
        • Wang Y.
        • Ding J.
        • Huang O.
        Diagnostic Indexes of a Rapid IgG/IgM Combined Antibody Test for SARS-CoV-2.
        MedRxiv. 2020; (doi: https://doi.org/)https://doi.org/10.1101/2020.03.26.20044883
        • Loeffelholz M.J.
        • Tang Y.W.
        Laboratory diagnosis of emerging human coronavirus infections – the state of the art.
        Emerg. Microbes. Infect. 2020; 9 (Dec): 747-756https://doi.org/10.1080/22221751.2020.1745095
        • Long Q.X.
        • Liu B.Z.
        • Deng H.J.
        • Wu G.C.
        • Deng K.
        • Chen Y.K.
        • Liao P.
        • Qiu J.F.
        • Lin Y.
        • Cai X.F.
        • Wang D.Q.
        • Hu Y.
        • Ren J.H.
        • Tang N.
        • Xu Y.Y.
        • Yu L.H.
        • Mo Z.
        • Gong F.
        • Zhang X.L.
        • Tian W.G.
        • Hu L.
        • Zhang X.X.
        • Xiang J.L.
        • Du H.X.
        • Liu H.W.
        • Lang C.H.
        • Luo X.H.
        • Wu S.B.
        • Cui X.P.
        • Zhou Z.
        • Zhu M.M.
        • Wang J.
        • Xue C.J.
        • Li X.F.
        • Wang L.
        • Li Z.J.
        • Wang K.
        • Niu C.C.
        • Yang Q.J.
        • Tang X.J.
        • Zhang Y.
        • Liu X.M.
        • Li J.J.
        • Zhang D.C.
        • Zhang F.
        • Liu P.
        • Yuan J.
        • Li Q.
        • Hu J.L.
        • Chen J.
        • Huang A.L.
        Antibody responses to SARS-CoV-2 in patients with COVID-19.
        Nat. Med. 2020; (Apr 29[Epub ahead of print] PubMed PMID:32350462)https://doi.org/10.1038/s41591-020-0897-1
        • Lou B.
        • Li T.D.
        • Zheng S.F.
        • Su Y.Y.
        • Li Z.Y.
        • Liu W.
        • Yu F.
        • Ge S.X.
        • Zou Q.D.
        • Yuan Q.
        • Lin S.
        • Hong C.M.
        • Yao X.Y.
        • Zhang X.J.
        • Wu D.H.
        • Zhou G.L.
        • Hou W.H.
        • Li T.T.
        • Zhang Y.L.
        • Zhang S.Y.
        • Fan J.
        • Zhang J.
        • Xia N.S.
        • Chen Y.
        Serology characteristics of SARS-CoV-2 infection since the exposure and post symptoms onset.
        medRxiv. 2020; (03.23.20041707; doi: https://doi.org/)https://doi.org/10.1101/2020.03.23.20041707
      5. Ma H., Zeng W., He H., Zhao D., Yang Y., Jiang D., et al., COVID-19 diagnosis and study of serum SARS-CoV-2 specific IgA, IgM and IgG by a quantitative and sensitive immunoassay 2020 doi: https://doi.org/10.1101/2020.04.17.20064907

        • Madsen T.
        • Levin N.
        • Niehus K.
        • Law K.
        • Mayer J.
        • Chapman M.
        • Johnson A.
        • Hartsell S.
        Prevalence of IgG antibodies to SARS-CoV-2 among emergency department employees.
        Am. J. Emerg. Med. 2020; (May 3. pii: S0735-6757(20)30306-5)
      6. Meyer B., Torriani G., Yerly S., Mazza L., Calame A., Arm-Vernez I. et al. Validation of a commercially available SARS-CoV-2 serological Immunoassay medRxiv 2020.05.02.20080879; doi: https://doi.org/10.1101/2020.05.02.20080879

        • Montesinos I.
        • Gruson D.
        • Kabamba B.
        • Dahma H.
        • Van den Wijngaert S.
        • Reza S.
        • Carbone V.
        • Vandenberg O.
        • Gulbis B.
        • Wolff F.
        • Rodriguez-Villalobos H.
        Evaluation of two automated and three rapid lateral flow immunoassays for the detection of anti-SARS-CoV-2 antibodies.
        J. Clin. Virol. 2020; 128 (May 5)104413https://doi.org/10.1016/j.jcv.2020.104413
      7. National COVID Testing Scientific Advisory Panel Evaluation of antibody testing for SARS-Cov-2 using ELISA and lateral flow immunoassay 2020 doi: https://doi.org/10.1101/2020.04.15.20066407

      8. Norman M., Gilboa T., Ogata F.A., Maley A.M., Cohen L., Cay Y. et al. Ultra-Sensitive High-Resolution Profiling of Anti-SARS-CoV-2 Antibodies for Detecting Early Seroconversion in COVID-19 Patients medRxiv 2020.04.28.20083691; doi: https://doi.org/10.1101/2020.04.28.20083691

        • Okba N.M.A.
        • Raj V.S.
        • Widjaja I.
        • GeurtsvanKessel C.H.
        • de Bruin E.
        • Chandler F.D.
        • et al.
        Sensitive and Specific Detection of Low-Level Antibody Responses in Mild Middle East Respiratory Syndrome Coronavirus Infections.
        Emerg. Infect. Dis. 2019; 25: 1868-1877
        • Ozturk T.
        • Howell C.
        • Benameur K.
        • Ramonell R.P.
        • Cashman K.
        Pirmohammed S Cross-sectional IgM and IgG profiles in SARS-CoV-2 infection.
        medRxiv. 2020; (05.10.20097535; doi: https://doi.org/)https://doi.org/10.1101/2020.05.10.20097535
        • Padoan A.
        • Cosma C.
        • Sciacovelli L.
        • Faggian D.
        • Plebani M.
        Analytical performances of a chemiluminescence immunoassay for 2019-nCov IgM/IgG and antibody kinetics.
        Clin. Chem. Lab. Med. 2020; https://doi.org/10.1515/cclm-2020-0443
        • Padoan A.
        • Sciacovelli L.
        • Basso D.
        • Negrini D.
        • Zuin S.
        • Cosma C.
        • Faggian D.
        • Matricardi P.
        • Plebani M.
        IgA-Ab response to spike glycoprotein of SARS-CoV-2 innpatients with COVID-19: A longitudinal study.
        Clin. Chim. Acta. 2020; 25 (507): 164-166
        • Pan Y.
        • Zhang D.
        • Yang P.
        • Poon L.L.M.
        • Wang Q.
        Viral load of SARS-CoV-2 in clinical samples.
        Lancet. Infect. Dis. 2020; 24: 30113-30114
        • Pan Y.
        • Li X.
        • Yang G.
        • Fan J.
        • Tang Y.
        • Zhao J.
        • Long X.
        • Guo S.
        • Zhao Z.
        • Liu Y.
        • Hu H.
        • Xue H.
        • Li Y.
        Serological immunochromatographic approach in diagnosis with SARS-CoV-2 infected COVID-19 patients.
        J. Infect. 2020; (pii: S0163-4453(20)30175-4)https://doi.org/10.1016/j.jinf.2020.03.05
        • Paradiso A.V.
        • De Summa S.
        • Silvestris N.
        • Tommasi S.
        • Tufaro A.
        • De Palma G.
        • Larocca A.M.V.
        • Chironna M.
        • D'Addabbo V.
        • Raffaele D.
        • Cafagna V.
        • Garrisi V.
        Rapid serological tests have a role in asymptomatic health workers COVID-19 screening.
        medRxiv. 2020; (04.15.20057786; doi: https://doi.org/)https://doi.org/10.1101/2020.04.15.20057786
        • Paradiso A.V.
        • De Summa S.
        • Loconsole D.
        • Procacci V.
        • Sallustio A.
        • Centrone F.
        • Silvestris N.
        • Cafagna V.
        • De Palma G.
        • Tufaro A.
        • Garrisi V.
        • Chironna M.
        Clinical meanings of rapid serological assay in patients tested for SARS-Co2 RT-PCR.
        medRxiv. 2020; (04.03.20052183; doi: https://doi.org/)https://doi.org/10.1101/2020.04.03.20052183
        • Perera R.A.
        • Mok C.K.
        • Tsang O.T.
        • Lv H.
        • Ko R.L.
        • Wu N.C.
        • Yuan M.
        • Leung W.S.
        • Chan J.M.
        • Chik T.S.
        • Choi C.Y.
        • Leung K.
        • Chan K.H.
        • Chan K.C.
        • Li K.C.
        • Wu J.T.
        • Wilson I.A.
        • Monto A.S.
        • Poon L.L.
        • Peiris M.
        Serological assays for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), March 2020.
        Euro. Surveill. 2020; 25 (Apr)https://doi.org/10.2807/1560-7917.ES.2020.25.16.2000421
        • Qian C.
        • Zhou M.
        • Cheng F.
        • Lin X.
        • Gong Y.
        • Xie X.
        • et al.
        Development and Multicenter Performance Evaluation of The First Fully Automated SARS-CoV-2 IgM and IgG Immunoassays.
        medRxiv. 2020; (doi.org/)https://doi.org/10.1101/2020.04.16.20067231
        • Qu J.
        • Wu C.
        • Li X.
        • Zhang G.
        • Jiang Z.
        • Li X.
        • Zhu Q.
        • Liu L.
        Profile of IgG and IgM antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
        Clin. Infect. Dis. 2020; (Apr 27. pii: ciaa489)https://doi.org/10.1093/cid/ciaa489
        • Rosado J.
        • Cockram C.
        • Merkling H.
        • Demeret C.
        • Meola A.
        • Kerneis S.
        Serological signatures of SARS-CoV-2 infection: Implications for antibody-based diagnostics.
        medRxiv. 2020; (05.07.20093963; doi: https://doi.org/)https://doi.org/10.1101/2020.05.07.20093963
        • Shakiba M.
        • Nazari S.
        • Mehrabian F.
        • Rezvani S.
        • Ghasempour Z.
        • Heidarzadeh A.
        Seroprevalence of COVID-19 virus infection in Guilan province, Iran.
        medRxiv. 2020; (04.26.20079244; doi: https://doi.org/)https://doi.org/10.1101/2020.04.26.20079244
        • Shen B.
        • Zheng Y.
        • Zhang X.
        • Zhang W.
        • Wang D.
        • Jin J.
        • Lin R.
        • Zhang Y.
        • Zhu G.
        • Zhu H.
        • Li J.
        • Xu J.
        • Ding X.
        • Chen S.
        • Lu R.
        • He Z.
        • Zhao H.
        • Ying L.
        • Zhang C.
        • Lv D.
        • Chen B.
        • Chen J.
        • Zhu J.
        • Hu B.
        • Hong C.
        • Xu X.
        • Chen J.
        • Liu C.
        • Zhou K.
        • Li J.
        • Zhao G.
        • Shen W.
        • Chen C.
        • Shao C.
        • Shen X.
        • Song J.
        • Wang Z.
        • Meng Y.
        • Wang C.
        • Han J.
        • Chen A.
        • Lu D.
        • Qian B.
        • Chen H.
        • Gao H.
        Clinical evaluation of a rapid colloidal gold immunochromatography assay for SARS-Cov-2 IgM/IgG.
        Am. J. Transl. Res. 2020; 12: 1348-1354
        • Silveira M.
        • Barros A.
        • Horta B.
        • Pellanda L.
        • Victora G.
        • Dellagostin O.
        • et al.
        Repeated population-based surveys of antibodies against SARS-CoV-2 in Southern Brazil.
        medRxiv. 2020; (05.01.20087205; doi: https://doi.org/)https://doi.org/10.1101/2020.05.01.20087205
        • Solodky M.L.
        • Galvez C.
        • Russias B.
        • Detourbet P.
        • N'Guyen-Bonin V.
        • Herr A.L.
        • Zrounba P.
        • Blay J.Y.
        Lower detection rates of SARS-COV2 antibodies in cancer patients vs healthcare workers after symptomatic COVID-19.
        Ann. Oncol. 2020; (Apr 30. pii: S0923-7534(20)39793-3)
        • Spicuzza L.
        • Montineri A.
        • Manuele R.
        • Crimi C.
        • Pistorio M.P.
        • Campisi R.
        • Vancheri C.
        • Crimi N.
        Reliability and usefulness of a rapid IgM-IgG antibody test for the diagnosis of SARS-CoV-2 infection: A preliminary report.
        J. Infect. 2020; (Apr 23. pii: S0163-4453(20)30231-0)https://doi.org/10.1016/j.jinf.2020.04.022
        • Sun B.
        • Feng Y.
        • Mo X.
        • Zheng P.
        • Wang Q.
        • Li P.
        • Peng P.
        • Liu X.
        • Chen Z.
        • Huang H.
        • Zhang F.
        • Luo W.
        • Niu X.
        • Hu P.
        • Wang L.
        • Peng H.
        • Huang Z.
        • Feng L.
        • Li F.
        • Zhang F.
        • Li F.
        • Zhong N.
        • Chen L.
        Kinetics of SARS-CoV-2 specific IgM and IgG responses in COVID-19 patients.
        Emerg. Microbes. Infect. 2020; 9: 940-948https://doi.org/10.1080/22221751.2020.1762515
        • Tang Y.W.
        • Schmitz J.E.
        • Persing D.H.
        • Stratton C.W.
        The Laboratory Diagnosis of COVID-19 Infection: Current Issues and Challenges.
        J. Clin. Microbiol. 2020; (pii: JCM.00512-20)https://doi.org/10.1128/JCM.00512-20
        • Tang M.S.
        • Hock K.G.
        • Logsdon N.M.
        • Hayes J.E.
        • Gronowski A.M.
        • Anderson N.W.
        • Farnsworth C.W.
        Clinical Performance of Two SARS-CoV-2 Serologic Assays.
        Clin. Chem. 2020; (May 13. pii: hvaa120[Epub ahead of print] PubMedPMID: 32402061)https://doi.org/10.1093/clinchem/hvaa120
        • Thompson C.
        • Grayson N.
        • Paton R.S.
        • Lourenco J.
        • Penman B.S.
        • Lee L.
        • et al.
        Neutralising antibodies to SARS coronavirus 2 in Scottish blood donors – a pilot study of the value of serology to determine population exposure.
        medRxiv. 2020; (04.13.20060467; doi: https://doi.org/)https://doi.org/10.1101/2020.04.13.20060467
        • To K.K.
        • Tsang O.T.
        • Leung W.S.
        • Tam A.R.
        • Wu T.C.
        • Lung D.C.
        • et al.
        Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study.
        Lancet Infect. Dis. 2020; https://doi.org/10.1016/S1473-3099(20)30196
        • Tosato F.
        • Pelloso M.
        • Gallo N.
        • Giraudo C.
        • Llanaj G.
        • Cosma C.
        • et al.
        2020 Severe Acute Respiratory Syndrome Coronavirus 2 Serology in Asymptomatic Healthcare Professionals: Preliminary Experience of a Tertiary Italian Academic Center.
        MedRxiv. 2020; (04.27.20073858; doi: https://doi.org/)https://doi.org/10.1101/2020.04.27.20073858
        • Tuaillon E.
        Detection of SARS-CoV-2 antibodies using commercial assays and seroconversion patterns in hospitalized patients.
        MedRxiv. 2020; (05.04.20090027; doi: https://doi.org/)https://doi.org/10.1101/2020.05.04.20090027
        • Wang X.
        • Guo X.
        • Xin Q.
        • Chu Y.
        • Li J.
        • Pan Y.
        • Feng Y.
        • Wang Q.
        Neutralizing Antibodies Responses to SARS-CoV-2 in COVID-19 Inpatients and Convalescent Patients.
        medRxiv. 2020; (04.15.20065623; doi: https://doi.org/)https://doi.org/10.1101/2020.04.15.20065623
        • Wajnberg A.
        • Mansour M.
        • Leven E.
        • Bouvier N.M.
        • Patel G.
        • Firpo A.
        • et al.
        Humoral immune response and prolonged PCR positivity in a cohort of 1343 SARS-CoV 2 patients in the New York City region.
        MedRxiv. 2020; (04.30.20085613; doi: https://doi.org/)https://doi.org/10.1101/2020.04.30.20085613
        • Wan Y.
        • Li Z.
        • Wank K.
        • Li T.
        • Liao P.
        Performance verification of detecting COVID-19 specific antibody by using four chemiluminescence immunoassay systems.
        medRxiv. 2020; (04.27.20074849; doi: https://doi.org/)https://doi.org/10.1101/2020.04.27.20074849
        • Wölfel R.
        • Corman V.M.
        • Guggemos W.
        • Seilmaier M.
        • Zange S.
        • Müller M.A.
        • Niemeyer D.
        • Jones T.C.
        • Vollmar P.
        • Rothe C.
        • Hoelscher M.
        • Bleicker T.
        • Brünink S.
        • Schneider J.
        • Ehmann R.
        • Zwirglmaier K.
        • Drosten C.
        • Wendtner C.
        Virological assessment of hospitalized patients with COVID-2019.
        Nature. 2020; https://doi.org/10.1038/s41586-020-2196-x
        • Watson J.
        • Whiting P.F.
        • Brush J.e.
        Interpreting a Covid-19 test results.
        BMJ. 2020; 369 (https://doi.org/)https://doi.org/10.1136/bmj.m1808
        • Won J.
        • Lee S.
        • Park M.
        • Kim T.Y.
        • Park M.G.
        • Choi B.Y.
        • Kim D.
        • Chang H.
        • Kim V.N.
        • Lee C.J.
        Development of a Laboratory-safe and Low-cost Detection Protocol for SARS-CoV-2 of the Coronavirus Disease 2019 (COVID-19).
        Exp. Neurobiol. 2020; https://doi.org/10.5607/en20009
        • Wu X.
        • Fu B.
        • Chen L.
        • Feng Y.
        Serological tests facilitate identification of asymptomatic SARS-CoV-2 infection in Wuhan, China.
        J. Med. Virol. 2020; (Apr 20)https://doi.org/10.1002/jmv.25904
        • Xiang F.
        • Wang X.
        • He X.
        • Peng Z.
        • Yang B.
        • Zhang J.
        • Zhou Q.
        • Ye H.
        • Ma Y.
        • Li H.
        • Wei X.
        • Cai P.
        • Ma W.L.
        Antibody Detection and Dynamic Characteristics in Patients with COVID-19.
        Clin. Infect. Dis. 2020; https://doi.org/10.1093/cid/ciaa461
        • Xiang J.
        • Yan M.
        • Li H.
        • Liu T.
        • Lin C.
        • Huang S.
        • Shen C.
        Evaluation of Enzyme-Linked Immunoassay and Colloidal Gold-Immunochromatographic Assay Kit for Detection of Novel Coronavirus (SARS-Cov-2) Causing an Outbreak of Pneumonia (COVID-19).
        medRxiv. 2020; (02.27.20028787; doi: https://doi.org/)https://doi.org/10.1101/2020.02.27.20028787
        • Xiao D.A.T.
        • Gao D.C.
        • Zhang D.S.
        Profile of Specific Antibodies to SARS-CoV-2: The First Report.
        J. Infect. 2020; https://doi.org/10.1016/j.jinf.2020.03.012
        • Yong G.
        • Yi Y.
        • Tuantuan L.
        • Xiaowu L.
        • Xiuyong L.
        • Ang L.
        • Mingfeng H.
        Evaluation of the auxiliary diagnosis value of antibodies assays for the detection of novel coronavirus (SARS-Cov-2).
        medRxiv. 2020; (03.26.20042044; doi: https://doi.org/)https://doi.org/10.1101/2020.03.26.20042044
        • Zhang J.
        • Liu J.
        • Li N.
        • Liu Y.
        • Ye R.
        • Qin X.
        • Zheng R.
        Serological detection of 2019-nCoV respond to the epidemic: A useful complement to nucleic acid testing.
        medRxiv. 2020; (03.04.20030916; doi: https://doi.org/)https://doi.org/10.1101/2020.03.04.20030916
      9. Zhao J., Yuan Q., Wang H., Liu W., Liao X., Su Y., et al. Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease 2019. Clin. Infect. Dis. doi:https://doi.org/10.1093/cid/ciaa344

        • Zhao R.
        • Li M.
        • Song H.
        • Chen J.
        • Ren W.
        • Feng Y.
        • Gao G.F.
        • Song J.
        • Peng Y.
        • Su B.
        • Guo X.
        • Wang Y.
        • Chen J.
        • Li J.
        • Sun H.
        • Bai Z.
        • Cao W.
        • Zhu J.
        • Zhang Q.
        • Sun Y.
        • Sun S.
        • Mao X.
        • Su J.
        • Chen X.
        • He A.
        • Gao W.
        • Jin R.
        • Jiang Y.
        • Sun L.
        Early detection of SARS-CoV-2 antibodies in COVID-19 patients as a serologic marker of infection.
        Clin. Infect. Dis. 2020; (May 1. pii: ciaa523)https://doi.org/10.1093/cid/ciaa523
        • Zhong L.
        • Chuan J.
        • Gong B.O.
        • Shuai P.
        • Zhou Y.
        • Zhang Y.
        • et al.
        Detection of serum IgM and IgG for COVID-19 diagnosis.
        Sci. China Life Sci. 2020; https://doi.org/10.1007/s11427-020-1688-9
        • Zou J.
        • Bretin A.
        • Gewirtz A.
        Antibodies to SARS/CoV-2 in arbitrarily-selected Atlanta residents.
        medRxiv. 2020; (05.01.20087478; doi: https://doi.org/)https://doi.org/10.1101/2020.05.01.20087478
        • Zou L.
        • Ruan F.
        • Huang M.
        • Liang L.
        • Huang H.
        • Hong Z.
        • Yu J.
        • Kang M.
        • Song Y.
        • Xia J.
        • Guo Q.
        • Song T.
        • He J.
        • Yen H.L.
        • Peiris M.
        • Wu J.
        SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients.
        N. Engl. J. Med. 2020; 382: 1177-1179
      10. Zhou Q., Zhu D., Yan H., Quan J., Kuang Z., Zhang, W. et al., A preliminary study on analytical performance of serological assay for SARS-CoV-2 IgM/IgG and application in clinical practice medRxiv 2020.05.05.20092551; doi: https://doi.org/10.1101/2020.05.05.20092551

        • Yangchun F.
        Optimize Clinical Laboratory Diagnosis of COVID-19 from Suspect Cases by Likelihood Ratio of SARS-CoV-2 IgM and IgG antibody.
        medRxiv. 2020; (04.07.20053660; doi: https://doi.org/)https://doi.org/10.1101/2020.04.07.20053660
        • Yong G.
        • Yi Y.
        • Tuantuan L.
        • Xiaowu W.
        • Xiuyong L.
        • Ang L.
        • Mingfeng H.
        Evaluation of the auxiliary diagnostic value of antibody assays for the detection of novel coronavirus (SARS-CoV-2).
        J. Med. Virol. 2020; (Apr 22)https://doi.org/10.1002/jmv.25919
        • Xiao T.
        • Wang Y.
        • Yuan J.
        • Ye H.
        • Wei L.
        • Wang H.
        • et al.
        Early viral clearance and antibody kinetics of COVID-19 among asymptomatic carriers.
        medRxiv. 2020; (04.28.20083139; doi: https://doi.org/)https://doi.org/10.1101/2020.04.28.20083139
        • Xie J.
        • Ding C.
        • Li J.
        • Wang Y.
        • Guo H.
        • Lu Z.
        • Wang J.
        • Zheng C.
        • Jin T.
        • Gao Y.
        • He H.
        Characteristics of patients with coronavirus disease (COVID-19) confirmed using an IgM-IgG antibody test.
        J. Med. Virol. 2020; (Apr 24)https://doi.org/10.1002/jmv.25930

      Biography

      Antonio La Marca is Professor of Obstetrics and Gynecology at the University of Modena and Reggio Emilia, Italy. His clinical activity covers all fields of reproductive medicine and surgery. He has published extensively; his current h-index is 44, with more than 8000 citations.
      Key Message
      Molecular and serological assays for SARS-CoV-2 are being developed and implemented at an exponential rate. This suite of complementary tests will inform crucial decisions by healthcare providers and policy makers and understanding their strengths and limitations will be critical to their judicious application to treatment and public health strategies.