Evaluation and comparison of four quantitative SARS-CoV-2 serological assays in COVID-19 patients and immunized healthy individuals, cancer patients, and patients with immunosuppressive therapy.

Background: Semi-quantitative and quantitative immunoassays are the most commonly used methodology to evaluate immunity post immunization.

Objectives: To compare four quantitative SARS-CoV-2 serological assays in COVID-19 patients and immunized healthy individuals, cancer patients, and patients with immunosuppressive therapy.

Study Design: 210 serological samples from COVID-19 infection and vaccination cohorts were used to create a serological sample repository. Serological methods from four manufacturers, namely Euroimmun, Roche, Abbott, and DiaSorin, were evaluated for quantitative, semi-quantitative, and qualitative antibody measurements. All four methods measure IgG antibodies against the SARS-CoV-2 spike receptor-binding domain and report the results in Binding Antibody Unit/mL (BAU/mL). A Total Error Allowable (TEa) of ±25% was chosen as the criteria to determine whether two methods are clinically equivalent quantitatively. Semi-quantitative results (titers) were derived using numeric antibody concentration divided by the cut-off value for each method.

Results: All paired quantitative comparisons demonstrated unacceptable performance. With ±25% as TEa, the best agreement was 74 (35.2% out of 210 samples) between Euroimmun and DiaSorin, whereas the lowest agreement was 11 (5.2% out of 210 samples) between Euroimmun and Roche. Antibody titers amongst all four methods were significantly different (p < 0.001). The highest titer difference from the same sample is between Roche and DiaSorin with a 1392-fold difference. On qualitative comparison, none of the paired comparison showed acceptable comparison (p < 0.001).

Conclusions: Poor correlation exists between four evaluated assays, quantitatively, semi-quantitatively, and qualitatively. Further harmonization of assays is required to achieve comparable measurements.