Comparison of SARS-CoV-2 Antibody Responses and Seroconversion in COVID-19 Patients Using Twelve Commercial Immunoassays

Abstract

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody assays have high clinical utility in managing the pandemic. We compared antibody responses and seroconversion of coronavirus disease 2019 (COVID-19) patients using different immunoassays.

Methods: We evaluated 12 commercial immunoassays, including three automated chemiluminescent immunoassays (Abbott, Roche, and Siemens), three enzyme immunoassays (Bio-Rad, Euroimmun, and Vircell), five lateral flow immunoassays (Boditech Med, SD biosensor, PCL, Sugentech, and Rapigen), and one surrogate neutralizing antibody assay (GenScript) in sequential samples from 49 COVID-19 patients and 10 seroconversion panels.

Results: The positive percent agreement (PPA) of assays for a COVID-19 diagnosis ranged from 84.0% to 98.5% for all samples (>14 days after symptom onset), with IgM or IgA assays showing higher PPAs. Seroconversion responses varied across the assay type and disease severity. Assays targeting the spike or receptor-binding domain protein showed a tendency for early seroconversion detection and higher index values in patients with severe disease. Index values from SARS-CoV-2 binding antibody assays (three automated assays, one LFIA, and three EIAs) showed moderate to strong correlations with the neutralizing antibody percentage (r=0.517-0.874), and stronger correlations in patients with severe disease and in assays targeting spike protein. Agreement among the 12 assays was good (74.3%-96.4%) for detecting IgG or total antibodies.

Conclusions: Positivity rates and seroconversion of SARS-CoV-2 antibodies vary depending on the assay kits, disease severity, and antigen target. This study contributes to a better understanding of antibody response in symptomatic COVID-19 patients using currently available assays.

Keywords: Correlation; Disease severity; Immunoassays; Neutralizing antibody; Positive percent agreement; SARS-CoV-2 antibody; Seroconversion.

Fig. 1

Seroconversion detected using eight antibody assays with corresponding index values. Serial serum samples from 10 patients hospitalized for confirmed SARS-CoV-2 infection were tested. The index values against days from symptom onset are plotted. The dotted horizontal line represents the assay cut-off for positivity. Patients with a severe (patients 1, 5, 9) and critical (patient 3) disease course are indicated in red and dark red, respectively. Patients with a mild disease course (patients 2, 4, 6, 7, 8, 10) are indicated in blue. (A) Abbott–IgG, (B) Siemens - Total Ig, (C) Roche–Total Ig, (D) Euroimmun–IgA, (E) Euroimmun–IgG, (F) Vircell–IgM+IgA, (G) Vircell–IgG, (H) Biorad–Total Ig. (I) Boditech–IgM, (J) Boditech–IgG, (K) Genscript –Neutralizing antibody.

Fig. 2

Correlations between antibody results by SARS-CoV-2 binding assays (three CLIAs, three EIAs, and one LFIA) and the neutralizing antibody results by sVNT. (A) Correlation between index values of SARS-CoV-2 IgG (Abbott; ratio, Siemens; index, Roche; log COI, Boditech; COI) and neutralizing antibody results (%) measured in 139 samples plotted according to disease severity. (B) Correlation between index values of SARS-CoV-2 IgG (Euroimmun; ratio, Vircell; index) or total antibody binding assays (BioRad; ratio) and neutralizing antibody results (%) measured in 109 samples plotted according to disease severity. The dotted line represents the assay cutoff for positivity. ^*P<0.001. Abbreviations: COI, cut-off index; r, Pearson correlation coefficient.