Analytical and clinical evaluation of four anti-SARS-CoV-2 serologic (IgM, IgG, and total) immunoassays

  1. Victoria Higgins
  2. Anselmo Fabros
  3. Xiao Yan Wang
  4. Maria Bhandari
  5. David J. Daghfal
  6. Vathany Kulasingam

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Abstract

Introduction

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is diagnosed by molecular-based detection of SARS-CoV-2 RNA. Serologic testing detects antibodies specific to SARS-CoV-2 and IgM specifically may serve as an adjunct test to PCR early in disease. We evaluated the Abbott anti-SARS-CoV-2 IgM and IgG assays along with DiaSorin anti-SARS-CoV-2 IgG and Roche anti-SARS-CoV-2 Total.

Methods

Specimens from 175 PCR-positive patients and 107 control specimens were analyzed using Abbott IgM and IgG, DiaSorin IgG, and Roche Total (IgA, IgG, IgM) assays. Sensitivity, specificity, cross-reactivity, concordance between assays, trends over time, positive predictive value (PPV), and negative predictive value (NPV) were determined.

Results

Abbott IgM sensitivity was 63.6% at 0 days post-PCR positivity, 76.5% at 1-5d, 76.3% at 6-14d, 85.2% at 15-30d, and 63.6% at >30d. All assays exhibited highest sensitivity 15-30d post-PCR positivity (83.3-85.2%). Combining Abbott IgM and IgG improved sensitivity by 22.7% compared to IgG alone when tested 0d post-PCR positivity. All assays had a specificity of 100% and only Abbott IgG exhibited cross-reactivity (anti-dsDNA). Cohen’s kappa varied between 0.86-0.93. Time to seroconversion from PCR positivity was lowest for Abbott IgM and highest for Abbott IgG. NPV was highest for Abbott IgM <14 days post-PCR positivity and Abbott IgG ≥14 days.

Conclusion

The Abbott IgM assay exhibited the earliest response and greatest signal in most patients evaluated for serial sampling and had the highest NPV <14 days post-PCR positivity, suggesting its potential utility as an adjunct test to PCR early in disease course.

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    SciScore for 10.1101/2020.10.23.20217810: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board StatementIRB: Sample Collection and Analysis: This work was exempt from Quality Improvement (QI) review and Research Ethics Board (REB) approval at the University Health Network (UHN; Toronto,
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    The anti-SARS-CoV-2 IgG assay detects IgG antibodies to the nucleocapsid protein of SARS-CoV-2, while the anti-SARS-CoV-2 IgM assay detects IgM antibodies to the receptor-binding domain (RBD) of the spike protein (S1) of SARS-CoV-2.
    anti-SARS-CoV-2 IgG assay detects IgG
    suggested: None
    anti-SARS-CoV-2 IgM assay detects IgM
    suggested: None
    Lastly, the Roche anti-SARS-CoV-2 total assay is a qualitative electrochemiluminescence immunoassay (ECLIA) that detects IgA, IgM and IgG antibodies to the nucleocapsid protein of SARS-CoV-2.
    IgG
    suggested: None
    Cross-reactivity & specificity: To determine the cross-reactivity of the four anti-SARS-CoV-2 antibody assays, serum or plasma samples were collected from 107 patients that were positive for viruses other than SARS-CoV-2 (e.g. hepatitis A, hepatitis B, hepatitis C, human immunodeficiency virus, rubella, Epstein-Barr virus, cytomegalovirus, respiratory syncytial virus, enterovirus, rhinovirus, influenza A, influenza B, metapneumovirus, BK virus), had autoantibodies or a known autoimmune condition (e.g. anti-dsDNA, rheumatoid factor, anti-centromere, anti-SSA, anti-Sm, anti-SmRNP, anti-RiboP, celiac disease, anti-MPO, anti-PR3, anti-CCP, antinuclear antibodies), had elevations of other analytes (e.g. creatinine, C-reactive protein, IgA, IgG, IgM), or had the influenza vaccine in 2019.
    anti-dsDNA, rheumatoid factor, anti-centromere, anti-SSA, anti-Sm, anti-SmRNP, anti-RiboP, celiac disease,
    suggested: None
    anti-MPO
    suggested: None
    anti-PR3
    suggested: None
    anti-CCP, antinuclear antibodies),
    suggested: None
    C-reactive protein, IgA, IgG, IgM
    suggested: None
    The percentage of samples that were incorrectly identified as positive for SARS-CoV-2 antibodies was determined for each assay.
    SARS-CoV-2
    suggested: None
    Software and Algorithms
    SentencesResources
    Deidentified residual patient serum and plasma samples were collected from UHN and analyzed using four anti-SARS-CoV-2 serologic assays at UHN, including SARS-CoV-2 IgG and SARS-CoV-2 IgM on the Abbott ARCHITECT® i (Abbott Diagnostics),
    Abbott
    suggested: (Abbott, RRID:SCR_010477)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Our study is not without limitations. Firstly, we did not collect information on the day of symptom onset due to confidentiality of personal health information, and thus all temporal data is only depicted as days since PCR positivity. This limits the accuracy of our assessment of sensitivity and antibody trends, as they are dependent on when the individual was tested for SARS-CoV-2 infection by PCR. However, this measure does reduce the potential subjectivity of using day of symptom onset as defined by each individual patient. Furthermore, as we did not collect information on clinical presentation and/or symptom severity, we are unable to make correlations between the assay signal and/or duration of antibody positivity with disease severity and/or patient outcome. In conclusion, we report a sensitivity of 87.5% 15-30 days post-PCR positivity, an overall specificity of 100%, and no cross-reactivity with patient samples containing autoantibodies, viral antigens, or viral antibodies for the Abbott anti-SARS-CoV-2 IgM assay. Combining Abbott anti-SARS-CoV-2 IgM and IgG testing improved sensitivity by 22.7% compared to IgG testing alone when tested the same day as PCR positivity. The Abbott anti-SARS-CoV-2 IgM assay exhibited the earliest response and greatest signal in the majority of patients evaluated with serial sampling and had the highest NPV <14 days post-PCR positivity, suggesting its potential utility as an adjunct test to PCR early in disease course.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

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  2. Version published to 10.1101/2020.10.23.20217810v1 on medRxiv