Objective: Analytical validation of newly released SARS-CoV-2 antibody assays in the clinical laboratory is crucial to ensure sufficient performance in respect to its intended use . We aimed to assess analytical and diagnostic performance of 8 (semi-) quantitative assays detecting anti-nucleocapsid IgG (Euroimmun, Id-Vet) or total Ig (Roche), anti-spike protein IgG (Euroimmun, Theradiag, DiaSorin, Thermo Fisher) or both (Theradiag) and 2 rapid lateral flow assays (LFA) (AAZ-LMB and Theradiag).

Methods: Specificity was evaluated using a cross-reactivity panel of 85 pre-pandemic serum samples . Sensitivity was determined at both the manufacturer's and a 95% specificity cut-off level, using 81 serum samples of patients with a positive rRT-PCR . Sensitivity was determined in function of time post symptoms onset .

Results: Specificity for all assays ranged from 92.9% to 100% (Roche and Thermo Fisher) with the exception of the Theradiag IgM LFA (82.4 %). Sensitivity in asymptomatic patients ranged between 41.7% and 58.3% . Sensitivity on samples taken <10 days since symptom onset was low (23.3% –66.7 %) and increased on samples taken between 10 and 20 days and> 20 days since symptom onset (80% –96% and 92.9% –100%, respectively). From 20 days after symptom onset, the Roche, Id-vet and Thermo Fisher assays all met the sensitivity (> 95 %) and specificity (> 97 %) targets determined by the WHO . Antibody signal response was significantly higher in the critically ill patient group . Conclusion: Antibody detection can complement rRT-PCR for the diagnosis of COVID-19, especially in the later stage, or in asymptomatic patients for epidemiological purposes . Addition of IgM in LFAs did not improve sensitivity.