An antigen test is a type of diagnostic test used to detect specific proteins, known as antigens, from a virus, such as the SARS-CoV-2 virus that causes COVID-19. These tests are typically quick and can provide results in as little as 15 to 30 minutes, making them useful for rapid screening in various settings. Antigen tests are often performed using a nasal swab or saliva sample. While they are generally less sensitive than PCR tests, they can be effective in identifying active infections, especially in individuals with high viral loads. However, negative results may require confirmation with a more sensitive test.