A serology test is a laboratory procedure used to detect and measure the presence of antibodies in the blood. These antibodies are proteins produced by the immune system in response to infections, vaccines, or other foreign substances. By analyzing a blood sample, healthcare providers can determine if a person has been exposed to specific pathogens, such as viruses or bacteria, and assess their immune response. Serology tests are commonly used for diagnosing diseases like HIV, hepatitis, and COVID-19. They can also help determine immunity to certain infections after vaccination. Results from these tests can guide treatment decisions and public health measures.