How do Rapid COVID-19 tests work?
COVID-19 rapid tests are a kind of test called a lateral flow immunoassay.
These tests detect the presence of the COVID-19 nucleocapsid protein (N protein) in the nasal swab sample you provide. The N protein is a part of the COVID-19 virus that helps it package its viral RNA and release viral particles from infected cells. Because this protein is found in all SARS-CoV viruses, it is used to tell if COVID-19 is present in your nasal swab sample or not.
The result of the COVID-19 test is displayed on a paper strip and is visualized on the test card by the presence or absence of a colored line. The sample well of the test strip contains a special gold-conjugated antibody that recognizes the N protein if present in your sample. This gold-conjugated antibody will grab onto any COVID-19 N protein in your sample and flow along with it across the paper as the liquid is drawn through the test strip. If the colored line appears in the “test” area, it’s because that gold-conjugated antibody gets stuck to another antibody affixed to the test area, causing an accumulation of colored particles which becomes visible.
If there is some N-protein but not enough in your sample, this can cause a faint test line. This is why it is important to view the test in good lighting. Additionally, you may consider repeating the test if it is negative and you are feeling ill.
When taking an antigen home test, ensure that you can see a solid control (C) line. Your test is invalid if a control line is not present, and you should try again with a fresh test.
Watch this video from WIRED that does a deep dive into the science behind the COVID-19 test for further explanation:
