Antigen testing is a type of diagnostic test that detects the presence of specific proteins, known as antigens, on or within a pathogen, such as a virus or bacteria. This type of testing is commonly used to quickly identify infections, particularly in the case of viral infections like COVID-19. Antigen tests are generally rapid and less expensive than other diagnostic tests, but may have lower sensitivity compared to molecular tests like PCR. Antigen testing is often used in combination with other diagnostic methods to help guide appropriate treatment and public health measures.