What is an Antigen Test?

When infected with SARS-CoV-2, the body produces antibodies that bind specifically to the spike proteins and other antigens to help eliminate the virus. This binding can be harnessed to develop antibody and antigen-based diagnostic tests. An antigen test reveals if a person is currently infected with a pathogen such as the SARS-CoV-2 virus. Once the infection has gone, the antigen disappears. 

Unlike nucleic acid based tests such as PCR, which detect the presence of genetic material, antigen tests detect proteins or glycans, such as the spike proteins found on the surface of the SARS-CoV-2 virus. 

Antigen tests usually provide test results rapidly, are relatively cheap, and can be more amenable to point-of-care use, which could make them more suitable for testing in the community and in remote regions. Antigen tests use a nasal or throat swab to detect viral proteins expressed on the outer surface of the coronavirus. 

The main selling points of antigen tests are that they are far faster and easier to perform than reverse transcriptase-polymerase chain reaction (PCR) tests. PCR tests – the swab tests that look for viral RNA – are currently the most common way of test for an active SARS-CoV-2 infection and can take up to four days to perform.

By contrast, the most time-consuming part of the antigen test process is waiting for the antibody mixtures and the sample to mix completely. This process takes mere minutes, given the small volumes typically used in an antigen test. A COVID-19 antigen test might take only 15-30 minutes to complete and requires very little expertise.

Similar tests have been done routinely in clinics for influenza all the time. In contrast, PCR tests swabs must be sent to diagnostic laboratories to be performed by experienced technicians as of right now.