Although positive results from rapid antigen tests are highly reliable, false negative results can occur if someone has a lower viral load — common early in the course of an infection. Rapid antigen tests are most reliable in the first week after symptoms start. However, if you have symptoms and test negative using a rapid test, you should not rule out COVID-19 infection. Taking a lab-based PCR test — which is able to detect smaller quantities of the virus and detect them sooner — can confirm your result and is necessary prior to coming to work if you have symptoms.
Every home in the U.S. is eligible to order four free at-home COVID-19 tests. They are also available at retail pharmacies. Community-based testing sites offer both rapid and lab-based tests, depending on the location. The CDC website provides additional details on COVID-19 diagnostic testing.
If you test positive or you have symptoms, call the Exposure/Illness Hotline at 314-362-5056. For more information, visit the Exposure & Illness Procedures page on the WashU Med coronavirus website.