The “gold standard” for clinical diagnostic detection of SARS-CoV-2 remains laboratory-based (moderate- and high-complexity) NAATs (PCR). Thus, it may be necessary to confirm an antigen test result with a laboratory-based NAAT, especially if the result of the antigen test is inconsistent with the clinical context. The sensitivity of antigen tests varies but is generally lower than most laboratory-based NAATs. The antigen level in specimens collected either before symptom onset, or late in the course of infection, may be below the tests’ limit of detection. This may result in a negative antigen test result, while a more sensitive test, such as most NAATs, may return a positive result.