Evaluation and comparison of eighteen SARS-CoV-2 antibody assays from seven different companies to assess its diagnostic role in SARS-CoV-2 infections.

The diagnostic performance of reverse transcriptase polymerase chain reaction (RT-PCR) decreases during the late acute stage of the corona virus disease (COVID-19) infection; hence, serological assays can be used for disease diagnosis in patients non-protected through vaccinations at this stage. The objective of this study was to assess the diagnostic accuracy of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody tests in current/past infections, determine proper testing time, and check the accuracy of cutoff values. In this study, 18 Ig (immunoglobulin) G, IgM, IgA, and total antibody serological assays were performed using 839 samples. Positive sera (n=132) were collected during the first 5 months after the patients were symptomatic and tested positive for the SARS-CoV-2 RT-PCR test; they were grouped as 0-10, 10-15, >15 days according to the symptom onset. Negative sera (N=707) were obtained from patients with lupus before the pandemic. The performance of IgG and total antibody assays was better than those of IgA, IgM, and IgA-IgM for all post-symptom groups except for 0-10 days, which showed lower Ig assay sensitivity. During 10-15 and >15 days, >70% sensitivity to IgA, IgM, IgM-IgA assays and lower sensitivity were noted, respectively. The sensitivities of IgG and total antibody assays for group C were slightly lower than that of group B. There were no significant differences, but there were higher correlations between the methods or antigenic structures. Receiving operating characteristics (ROC) analysis revealed better cutoff values. For the diagnosis of late acute/past SARS-CoV-2 infection, serological tests can be performed on unvaccinated patients showing symptoms for ≥10 days. SARS-CoV-2 IgG and total antibodies were better diagnostic markers than IgM, IgA, and IgM+IgA, which were restricted to group B.