Commercially available SARS-CoV-2-directed antibody assays may assist in diagnosing past exposure to SARS-CoV-2 antigens. We cross-compared the following eight immunoassays detecting antibodies against SARS-CoV-2 nucleocapsid (N) or spike (S) antigens in three cohorts consisting of 859 samples from 622 patients: (#1) EDI novel coronavirus COVID-19 (Epitope), (#2) RecomWell SARS-CoV-2 (Mikrogen), (#3) COVID-19 ELISA (VirCell), (#4) Elecsys anti-SARS-CoV-2 N (Roche), (#5) Liaison SARS-CoV-2 S1/S2 (DiaSorin), (#6) anti-SARS-CoV-2 ELISA (EuroImmun), (#7) Elecsys anti-SARS-CoV-2 S (Roche), and (#8) Liaison SARS-CoV-2 TrimericS (DiaSorin). In cross-sectional cohort 1 (68 sera from 38 patients with documented SARS-CoV-2 infection), agreement between assays #1 to #6 ranged from 75% to 93%, whereby discordance mostly resulted from N-based assays #1 to #4. In cross-sectional cohort 2 (510 sera from 510 patients; 56 documented, 454 unknown SARS-CoV-2 infection), assays #4 to #6 were analyzed further together with assays #7 and #8, revealing 94% concordance (44 [9%] positives and 485 [85%] negatives). Discordance was highest within 2 weeks after SARS-CoV-2/COVID-19 diagnosis and confirmed in the longitudinal cohort 3 (281 sera from 74 COVID-19 patients), using assays #4, #6, #7, and #8. Subanalysis of 20 (27%) initially seronegative cohort 3 patients revealed assay-dependent 50% and 90% seroconversion rates after 8 to 11 days and 14 to 18 days, respectively. Increasing SARS-CoV-2 antibodies were significantly associated with declining levels of viral loads, lactate dehydrogenase, interleukin-6, and C-reactive protein and preceded clearance of SARS-CoV-2 detection in the upper respiratory tract by approximately 1 week. SARS-CoV-2-specific antibody assays show substantial agreement, but interpretation of qualitative and semiquantitative results depends on the time elapsed postdiagnosis and the choice of viral antigen. Mounting of systemic SARS-CoV-2-specific antibodies may predict recovery from viral injury and clearance of mucosal replication.
Keywords: COVID-19; antibody; nucleocapsid; seroconversion; spike.