Diagnostic performance of the Elecsys SARS-CoV-2 antigen assay in the clinical routine of a tertiary care hospital: Preliminary results from a single-center evaluation

Abstract

Background: This 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. Methods: In 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. Results: Of 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. Conclusions: The 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.