Pitfalls of SARS-CoV-2 antigen testing at emergency department

Background Current method for diagnosis of SARS-CoV-2 infection is an RT-PCR test on the nasopharyngeal or oropharyngeal swab. Rapid diagnosis is essential for containing viral spread and triage of symptomatic patients presenting to hospital ER departments. As a faster alternative to RT-PCR, we evaluated a SARS-Cov-2 Rapid Antigen test in symptomatic patients presenting to hospital ER departments. Methods We evaluated the diagnostic performance of the Roche SARS-CoV-2 Rapid Antigen test (SD Biosensor) for detection of SARS-CoV-2 compared to RT-PCR. Results Our study showed inferior performance of the SARS-CoV-2 Rapid Antigen test for detection of SARS-CoV-2. Firstly, because of the lack of specificity, which is potentially life-threatening due to the association of nosocomial-acquired SARS-CoV-2 infection. Secondly, with a sensitivity of 45.5%, it is impossible to rule out SARS-CoV-2 infection, resulting in reflex PCR-testing. Comparison of viral load in RT-PCR positive samples with corresponding antigen results showed a significant difference between antigen positive and negative samples. COVID-19 infection will not be detected in patients admitted to the hospital in an early or late phase, typically associated with low viral loads. Sensitivity increases when testing within 5-7 symptomatic days, but the implementation of this cut-off is impractical in ER settings. However, diagnostic performance is better to detect high viral load (> = 5 log10 copies/mL) linked with contagiousness. Conclusion Our study showed inferior performance of the Roche SARS-CoV-2 Rapid Antigen test (SD Biosensor) for detection of SARS-CoV-2 which limits its use as a diagnostic gatekeeper in ER departments, but is able to differentiate contagious individuals.