Sensitivity Affected by Disease Severity and Serum Sampling Time: a Performance Evaluation of Six SARS-CoV-2 Antibody Immunoassays.

Comparative validation and clinical performance data are essential for the reliable interpretation of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antibody test results. This study aimed to assess the performance of six SARS-CoV-2 IgG immunoassays in the context of different disease severities. Four automated chemiluminescence immunoassays (Access [Beckman Coulter], Architect [Abbott], Atellica-IM [Siemens], and Elecsys [Roche]) as well as two ELISA assays (SARS-CoV-2 IgG-S1-based and NCP IgG [Euroimmun]) were evaluated using samples from 143 patients as well as 50 pre-pandemic control serum samples. Accuracy and precision tests were performed for validation purposes. Overall sensitivity ranged between 73.38-88.65% and was higher in spike protein-based assays, while the specificity was ≥98% in all immunoassays. The clinical performance of the immunoassays differed depending on disease severity and target antigen. For instance, the IgG response was lower for samples taken <20 days post-symptom onset (87.30%) compared with those taken ≥20 days post-symptom onset (94.80%). Moreover, moderate disease levels led to the highest levels of IgG. Higher levels of antibodies were detected in the clinically moderate disease group. In asymptomatic and mild groups, more antibody positivity was detected with spike protein-based assays. All the assays tested could be used to detect SARS-CoV-2 IgG. However, spike-based assays revealed relatively higher sensitivity rates than nucleoprotein-based assays, particularly in cases of asymptomatic and mild disease.