Evaluation of 3 SARS-CoV-2 IgG Antibody Assays and Correlation with Neutralizing Antibodies

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 3 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.

Three panels of samples were tested on every assay. Sensitivity was assessed using a panel of 35 specimens serially collected from 7 patients with RT-PCR-confirmed COVID-19. 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.

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.

The 3 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.