Evaluation of the Elecsys SARS-CoV-2 antigen assay for the detection of SARS-CoV-2 in nasopharyngeal swabs

•Antigen assays for the detection of SARS-CoV-2 are relatively inexpensive and take less time than RT-PCR.The automated Elecsys® SARS-CoV-2 antigen was evaluated compared to the gold standard RT-PCR•Overall sensitivity of the automated Ag test was 65,85% but could be increased to 100% for Ct values 0,673 COI, the accuracy reached its highest level with a sensitivity of 74,8% (95% CI 66,2 – 82,2%) and a specificity of 97,1% (95% CI 91,6 – 99,4%). Imprecision was estimated in accordance with manufacturer's claims. We obtained an overall sensitivity of 65,85% (95% CI 56,76–74,16%) and a specificity of 100% (95% CI 96,49–100%), slightly higher than the results reported by the manufacturer. Yet, it remains relatively low comparatively to what is generally acceptable for these antigenic assays (a relative sensitivity of 80%). We also noticed that the accuracy could reach its highest level if the cut-off is set above 0,673 which is lower than established by the manufacturer. Thus, our results suggest that the Elecsys® SARS-CoV-2 Antigen assays, should be improved prior to be used in a SARS-Cov-2 screening strategy. However, if one antigenic assay could demonstrate acceptable performance, it might be centralized in clinical laboratories, keeping the RT-PCR in a second phase for confirmation.