• Thomas Mueller, Julia Kompatscher, and Mario La Guardia.
• Department of Clinical Pathology, Hospital of Bolzano, Bolzano, Italy.
• J. Clin. Lab. Anal. 2021 Aug 1; 35 (8): e23906.

BackgroundThis report describes a manufacturer-independent evaluation of the diagnostic accuracy of the Elecsys SARS-CoV-2 antigen assay from Roche Diagnostics in a tertiary care setting.MethodsIn this single-center study, we used nasopharyngeal swabs from 403 cases from the emergency department and intensive care unit of our hospital. The reference standard for detecting SARS-CoV-2 was the reverse-transcription polymerase chain reaction (RT-PCR) assay. Cycle threshold (Ct) values were recorded for positive RT-PCR assays. The index test was the Elecsys SARS-CoV-2 antigen assay. This electrochemiluminescence immunoassay produces results as cutoff index (COI) values, with values ≥1.00 being reported as positive.ResultsOf the 403 cases, 47 showed positive results in RT-PCR assays. Of the 47 RT-PCR-positive cases, 12 showed positive results in the antigen assay. Of the 356 RT-PCR-negative cases, all showed negative results in the antigen assay. Thus, the antigen assay showed a sensitivity of 26% (95% CI, 14%-40%) and specificity of 100% (95% CI, 99%-100%). Analysis of the relationship between Ct values and COI values in the 47 RT-PCR-positive cases showed a correlation coefficient of -0.704 (95% CI, -0.824 to -0.522). The true-positive rate of the antigen assay for Ct values of 15-24.9, 25-29.9, 30-34.9, and 35-39.9 was 100%, 44%, 8%, and 6%, respectively.ConclusionsThe Elecsys SARS-CoV-2 antigen assay has a low sensitivity for detecting SARS-CoV-2 from nasopharyngeal swabs. Hence, we decided to not use this assay in the clinical routine of our hospital.© 2021 The Authors. Journal of Clinical Laboratory Analysis published by Wiley Periodicals LLC.

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