Currently, there are two ways to test for the virus that causes COVID-19: molecular testing (PCR) and antigen testing. PCR testing has been used since the pandemic began and is considered to be the “gold standard“ by the Centers for Disease Control and Prevention (CDC).
COVID-19 antigen tests are designed for the rapid diagnoses of active infection primarily by detecting the nucleocapsid protein antigen of the SARS-CoV-2 virus (the virus that causes COVID-19) from nasal swabs or similar clinical specimens. After collection, point-of-care antigen tests take approximately 15-30 minutes to finalize a result.
Antigen tests are generally less sensitive than PCR tests. Because of the lower sensitivity, false negative antigen test results are possible and testing is most accurate when there is a high pre-test probability of SARS-CoV-2 infection like high prevalence of infection in the community or a patient who showing symptoms of COVID-19. In addition, viral carriage is highest early in infection; therefore, antigen tests are more likely to detect a true positive early in infection.
Single antigen tests, done at one point in time, are typically meant to be used within 5-7 days after symptoms begin showing, though at least one test allows for testing more than 7 days after symptoms begin showing. Please contact your medical provider or refer to the manufacturer’s instructions for the appropriate time window for the test being used.
Between late March and early April 2021, the Food and Drug Administration (FDA) issued multiple Emergency Use Authorizations for serial antigen testing products. Although the same test devices are used, serial antigen tests have important differences compared to single antigen tests. Serial antigen tests consist of doing two antigen tests over a 2-3 day time period, with an interval of 24-36 hours between tests. FDA expanded the indications for serial antigen tests - they can be used for diagnostic purposes in people suspected of having COVID-19 based on symptoms or for screening testing in asymptomatic people or those who are a close contact. A number of serial antigen test productions are nonprescription items. FDA's authorization of serial antigen testing products greatly expands the indications for testing as well as public access to testing products.*
Providers conducting antigen tests on either symptomatic or asymptomatic populations must be aware of the potential for false-negative or false-positive results. When the result of an antigen test does not fit the clinical circumstances of the patient, a PCR test is recommended for confirmation of the antigen test result.
When should you use an Antigen Test?
- If you are showing symptoms of COVID-19, particularly within 7 days of showing symptoms. Testing can be done regardless of vaccination status.
- If you are not fully vaccinated and have close contact to someone with known or suspected COVID-19. Testing should happen as soon as the individual knows of close contact exposure, and if negative, should test again between 5-7 days after the last known exposure, immediately or if symptoms develop.
- If you’re not showing symptoms of COVID-19 and are fully vaccinated and have close contact to someone with known or suspected COVID-19. Testing should occur 5-7 after the exposure.
- If you’re showing symptoms and you’re a resident or staff in congregate settings like nursing homes and correctional facilities. Testing should be done regardless of vaccination status.
- If you’re not showing symptoms of COVID-19 and are not a close contact to a known COVID-19 case.
- If you’re not showing symptoms of COVID-19 and you participated in high-risk activities where you could not physically distance like traveling, attending large social or mass gatherings, or being in a crowded indoor setting)
Where do I report my test results?
Visit coronavirus.dc.gov/overthecounter to report your self-test result.
*The clinical performance of serial antigen testing as a means of screening for COVID-19 has not been determined. This is noted in the instructions for use of each serial antigen testing product, and it is stated that a study to support use will be completed.
Adapted from Virginia Department of Health's Antigen Testing Recommendations