Antibody testing is a medical procedure used to determine if a person has been exposed to a specific virus or bacteria, such as the SARS-CoV-2 virus that causes COVID-19. This test detects antibodies in the blood, which are proteins produced by the immune system in response to an infection. A positive result indicates past exposure, while a negative result suggests no exposure or that the immune response has not yet developed. These tests are often used for public health purposes, helping to understand the spread of infections within a community. However, antibody tests are not used to diagnose active infections, as they do not indicate current illness.