Comparison of indigenous enzyme-linked immunosorbent assay and chemiluminescent immunoassays for screening for immunoglobulin G antibodies against SARS-CoV-2 in India

Serological screening for antibody against SARS-CoV-2 has been gaining more attention in view of selection for an appropriate donor for COVID-19 convalescent plasma, documenting the past/ recent infection due to the virus as well as now for evaluating the immune response to the vaccination. In beginning of the pandemic an indigenous ELISA kits were developed in India to screen for IgG type of antibody against the whole-cell virus particle. Our retrospective analysis provides a head-to-head comparison of an indigenous ELISA kits (COVID KAWACH IgG MICROLISA) and CLIA (SARS-CoV-2 IgG by Abbott) platform for screening of IgG type of antibody. Total 380 samples from adults were screened on both the platforms, out of which 250 had a history of a positive RT-PCR report and 130 were RT-PCR negative but with a history of symptoms suggestive of COVID-19 or exposure to COVID-19 individual. The overall concordance of detection IgG type of antibody by both the platforms was 52.2% (higher in individuals with known RT-PCR positivity; 70%). The median S/CO ratio (on CLIA) was 3.34 in concordant positive samples and 2.48 in cases of CLIA yield samples. Our study highlights the variation in detection of the antibody by both the platforms due to inherent difference in the design of these platforms and kits.