Early detection of SARS-CoV-2 patients is essential to contain the pandemic and keep the hospital secure. The rapid antigen test seems to be a quick and easy diagnostic test to identify patients infected with SARS-CoV-2. To assess the possible role of the antigen test in the Emergency Department (ED) assessment of potential SARS-CoV-2 infection in both symptomatic and asymptomatic patients.

Between 1 July 2020 and 10 December 2020, all patients consecutively assessed in the ED for suspected COVID-19 symptoms or who required hospitalisation for a condition not associated with COVID-19 were subjected to a rapid antigen test and RT-PCR swab. The diagnostic accuracy of the antigen test was determined in comparison to the SARS-CoV-2 PCR test using contingency tables. The possible clinical benefit of the antigen test was globally evaluated through decision curve analysis (DCA).

A total of 3899 patients were subjected to antigen tests and PCR swabs. The sensitivity, specificity and accuracy of the antigen test were 82.9%, 99.1% and 97.4% (Cohen's K = 0.854, 95% CI 0.826–0.882, p < 0.001), respectively. In symptomatic patients, sensitivity was found to be 89.8%, while in asymptomatic patients, sensitivity was 63.1%. DCA appears to confirm a net clinical benefit for the preliminary use of antigen tests.

The antigen test performed in the ED, though not ideal, can improve the overall identification of infected patients. While it appears to perform well in symptomatic patients, in asymptomatic patients, although it improves their management, it seems not to be definitive.