Antigen tests are done by looking for proteins on the surface of the virus to ascertain the presence of the pathogen. The test requires a swab from the back of your nose or throat as a sample and cannot determine whether you are contagious if positive.
Antigen tests — often referred to as rapid tests — work by mixing the sample with a solution that unleashes specific viral proteins. That combination is then applied to a paper strip that contains a bespoke antibody optimized to bind these proteins if they are present. Like in a home pregnancy test, the result is reflected as a band on the paper strip.
The process doesn’t require a lab, and can be done in up to 30 minutes, but that speed comes at the cost of sensitivity. Although these tests are reliable when an individual has a high viral load, they are far more prone to generating false-negative results if a person has low amounts of the virus in their body.