The tests detect specific proteins — known as antigens — on the surface of the virus, and can identify people who are at the peak of infection, when virus levels in the body are likely to be high.
Antigen assays are much faster and cheaper than the gold-standard tests that detect viral RNA using a technique called the polymerase chain reaction (PCR). But antigen tests aren’t as sensitive as the PCR versions, which can pick up minuscule amounts of the SARS-CoV-2 virus that causes COVID-19. Results in 15 mins