SARS‐CoV‐2 rapid antigen test: Fast‐safe or dangerous? An analysis in the emergency department of an university hospital

The use of Antigen point of care tests (AgPOCT) might be an essential tool to fight the coronavirus disease 2019 (COVID‐19) pandemic. Manufacturer information indicates a specificity of about 95% and there is a growing interest to use these tests area‐wide. Therefore, it is necessary to clarify whether AgPOCT can be used safely for “rule‐in” (detection of positive patients) and for “rule‐out” (valid negative testing). Two thousand three hundred and seventy‐five patients received polymerase chain reaction (PCR) testing and AgPOCT for severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) regardless of symptoms. The positive predictive value of symptomatic and asymptomatic patients was compared with a cut‐off threshold cycle (C (t)) value of ≤30 and in total. Five hundrded and fifty‐one patients tested positive for the SARS‐CoV‐2 virus by PCR, of whom 35.2% presented without symptoms. In all patients, regardless of their symptoms or C (t) values, a sensitivity of 68.9% and a specificity of 99.6% were calculated for AgPOCT. In patients with C (t) values ≤30, a sensitivity of 80.5% (95% confidence interval: ±1.62) and a specificity of 99.6% were shown for all tests (symptomatic/asymptomatic). Highly infectious patients (C (t) ≤ 20), regardless of symptoms, were reliably detected by the AgPOCT. In infectious patients with C (t) values ≤30, the test has a sensitivity of about 80% regardless of COVID‐19 typical symptoms, which is apparently less than the 96.52% specificity indicated by the manufacturer. Relevant improvement in test sensitivity by querying the patients who are symptomatic and asymptomatic is also not feasible. We strongly suggest that we critically question the use of AgPOCT for “rule‐out,” as they only provide a supposed safety.