Interpretation of Positive Roche Elecsys SARS-CoV-2 Antigen Test Results: Value for Clinical Decisions

The Elecsys SARS-CoV-2 antigen test (Elecsys; Roche Diagnostics, Rotkreuz, Switzerland) is a quantitative test for detecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen. Although the positive predictive value of the test is high, false-positive (FP) results are unavoidable. Furthermore, FP results can lead to unnecessary isolation of patients or exposure of FP patients to truly positive patients. Therefore, to minimize potential harm to FP patients, this study aimed to identify clinical cases that are likely to produce FP results and in which additional testing should be recommended. These recommendations should be based on the Elecsys test results and relevant clinical information. Correspondingly, a retrospective study was conducted using nasopharyngeal swab samples from symptomatic and asymptomatic patients with SARS-CoV-2 infection and patients who had close contact with a confirmed SARS-CoV-2 infection case between September 2021 and October 2023. Of the total 5989 samples, 302 tested positive in the Elecsys test. Thereafter, the reverse transcription-polymerase chain reaction test was performed on patient samples (n = 54) with positive Elecsys test results without clinical information consistent with coronavirus disease 19 (COVID-19). A total of 37 of these samples were FP results, and all FP samples showed Elecsys test values near the cutoff index (COI) value. Accordingly, when the Elecsys test yields a low COI value, and the clinical presentation is inconsistent with COVID-19, additional confirmatory testing is recommended.