Comparative validation data and clinical performance data are essential for the reliable interpretation of SARS-CoV-2 antibody test results. This study aimed to assess the performance of six SARS-CoV-2 IgG immunoassays in different disease severity settings.Four automated chemiluminescence immunoassays Access (Beckman Coulter), Architect (Abbott), Atellica-IM (Siemens) and Elecsys (Roche) and two ELISA assays (SARS-CoV-2 IgG-S1-based and NCP IgG, Euroimmun) were evaluated in 143 patients and 50 pre-pandemic control sera. Accuracy and precision tests were performed for validation. Overall sensitivity differed between 73.38-88.65%, being higher in spike protein-based assays.Specificity was > 98% in all immunoassays. IgG response was lower for the samples taken <20 days post-symptom onset (87.30%) than for the samples taken >20 days postsymptom onset (94.80%). Higher rate of antibody was detected in the clinically moderate disease group. In the asymptomatic and mild group more antibody positivity was detected with spike protein-based assays. Clinical performance of the immunoassays differs according to disease severity and antigen targeted; moderate disease leading to highest rate of IgG response. All the assays tested were eligible for the detection of SARS-CoV-2 IgG however, spike-based assays revealed relatively higher sensitivity than the nucleoprotein-based assays particularly in the asymptomatic and mild disease severity.

Objective: The reverse transcription–polymerase chain reaction test (RT-PCR) is the gold standard for the diagnosis of coronavirus disease 2019 (COVID-19), and antibody tests are useful as supplemental tools for diagnosis, for measuring the population’s immunity levels, and for checking infection in asymptomatic contacts. This study aimed to evaluate the reliability of five commercial antibody detection test kits. Materials and Methods: The reliability of the Colloidal Gold COVID-19 IgG/IgM Rapid Test Kit, Antibody Rapid Test Hotgen, Beijing Hotgen Biotech Co., Ltd., China), Abbott Chemiluminescent Microparticle Immunoassay (Illinois, USA), Roche Electrochemiluminescence Immunoassay (Roche Diagnostics, Switzerland), Siemens Chemiluminescence (Munich, Germany), and Euroimmun ELISA (Lübeck, Germany) for COVID-19 diagnosis was studied. The antibody-negative group included 50 sera from 2018, and the antibody-positive group included 98 patients with positive RT-PCR results from whom blood samples had been collected 3–9 weeks after hospital discharge. Statistical analysis was performed using SPSS version 23.0 (IBM Corporation, Armonk, NY, USA). The antibody tests’ validity and intra-assay reproducibility were examined, and the Cohen’s kappa coefficients were obtained. The disease prevalence was pegged at 10%. Results: The antibody tests’ sensitivity (69.12–72.46%) and positive predictive values (42.44–100.0%) were low, and their specificity (89.58–100%) and negative predictive values (96.31–97.03%) were high. Their accuracy rates varied from 87.54% to 97.25%, and their intra-assay coefficients of variation varied from 1% to 10%. Conclusion: The agreement between the results of the antibody detection test kits was higher when the kits were classified according to the targeted antigens. The time of blood sample collection, targeted antigens, and antibody types affected the results. Serological tests were found to be useful, and the commercial kits were found to be largely reliable, although, some parameters need to be improved.