Evaluation of Three SARS CoV-2 IgG Antibody Assays and Correlation with Neutralizing Antibodies

BACKGROUND: As serologic assays for SARS-CoV-2 become more widely utilized, it is important to understand their performance characteristics and correlation with neutralizing antibodies We evaluated three commonly used SARS-CoV-2 IgG assays (Abbott, DiaSorin and EUROIMMUN) for clinical sensitivity, specificity, and correlation with neutralizing antibodies and then compared antibody kinetics during the acute phase of infection METHODS: Three panels of samples were tested on every assay Sensitivity was assessed using a panel of 35 specimens serially collected from 7 RT-PCR-confirmed COVID-19 patients Specificity was determined using 100 sera samples collected in 2018 from healthy individuals prior to the outbreak Analytical specificity was determined using a panel of 37 samples from individuals with respiratory illnesses other than COVID-19 RESULTS: Clinical sensitivity was 91 43% (95% CI 76 94%-98 20%) for Abbott, and 88 57% (95% CI 73 26%-96 80%) for both DiaSorin and EUROIMMUN Clinical specificity was 99 00% (95% CI 94 55%-99 97%) for Abbott and DiaSorin and 94 00% (95% CI 87 40%-97 77%) for EUROIMMUN The IgG assays demonstrated good qualitative agreement (minimum of 94%) and good correlation between the quantitative result for each combination of assays (r2≥0 90) The neutralizing antibody response did not necessarily follow the same temporal kinetics as the IgG response and did not necessarily correlate with IgG values CONCLUSION: The three IgG antibody assays demonstrated comparable performance characteristics Importantly, a qualitative positive IgG result obtained with any of the assays was associated with the presence of neutralizing antibodies;however, neutralizing antibody concentrations did not correlate well with signal to cutoff ratios