Antibody or serology tests look for antibodies in your blood to determine if you had a past infection with the virus that causes COVID-19. - Antibodies are proteins created by your body’s immune system soon after you have been infected or vaccinated. - Antibodies help you fight off infections and can protect you from getting that disease again. How long this protection may last is different for each disease and each person. Antibody tests should not be used to diagnose a current infection with the virus that causes COVID-19.  An antibody test may not show if you have a current infection because it can take 1–3 weeks after the infection for your body to make antibodies. (Source: CDC) Results are usually ready the same day.