The Infectious Diseases Society of America Guidelines on the Diagnosis of COVID-19: Antigen Testing (June 2021).

This article focuses on evidence-based guidelines developed by the Infectious Diseases Society of America (IDSA) regarding the use of SARS-CoV-2 antigen (Ag) tests authorized under the US Food and Drug Administration Emergency Use Authorization (FDA-EUA). The guidelines, based on a systematic review and GRADE methodology, recommend standard nucleic acid amplification tests (NAAT), including rapid reverse transcriptase–polymerase chain reaction (RT-PCR) and laboratory-based NAAT, over rapid Ag tests for diagnosing COVID-19 in symptomatic individuals and for screening asymptomatic individuals at risk of exposure, due to higher sensitivity of NAAT. Rapid Ag tests, which provide results in about 15 minutes and have high specificity (~99%), may be used when NAAT is unavailable or delayed, but negative Ag results in symptomatic persons should be confirmed by NAAT. The panel also addresses testing strategies involving single versus repeat Ag tests in asymptomatic individuals, highlighting evidence gaps and emphasizing individualized decisions based on factors such as disease prevalence, vaccination status, and testing feasibility. Overall, while rapid Ag tests expand testing accessibility, especially in nonmedical settings, NAAT remains the preferred diagnostic method when accuracy is critical.