Test for Past Infection

Antibody or serology tests look for antibodies in your blood that fight the virus that causes COVID-19.

• Antibodies are proteins created by your immune system that help you fight off infections. They are made after you have been infected or have been vaccinated against an infection.
• Antibodies help you fight off infections and can protect you from getting that infection for some period of time afterward. How long this protection lasts is different for each disease and each person.­
• Antibody tests should generally 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 to 3 weeks after the infection for your body to make antibodies.
• Whether you test positive or negative for COVID-19 on a viral or an antibody test, you still should take steps to protect yourself and others.

Decisions about testing are made by state or localexternal icon health departments or healthcare professionals.

Antibody tests for COVID-19 are available through healthcare professionals and laboratories. Check with your healthcare professional to see if they offer antibody tests and whether you should get one.

What your results mean?

If you test positive

• A positive antibody test result shows you may have antibodies from a previous infection with the virus that causes COVID-19.
• Antibodies to the virus that causes COVID-19 provide protection from getting infected. CDC is evaluating how long protection from antibodies might last. Cases of reinfection have been reported, but remain rare.
• You may test positive for antibodies even if you have never had symptoms of COVID-19. This can happen if you had an infection without symptoms, which is called an asymptomatic infection.
• Sometimes a person can test positive for SARS-CoV-2 antibodies when they do not actually have those specific antibodies. This is called a false positive.
• Talk with your healthcare professional about your test result and the type of test you took to understand what your result means. Your healthcare professional may suggest you take a second type of antibody test to see if the first test was accurate.

If you test negative

• You may not have COVID-19 antibodies. This could be because you have not had an infection with the virus that causes COVID-19.
• You could have a current infection, been recently infected, or been recently vaccinated. It typically takes 1 to 3 weeks after infection for your body to make antibodies. If you are infected, you may get sick and spread the virus before you develop antibodies.
  • Some people may take even longer to develop antibodies, and a small portion of people who are infected or vaccinated may never develop antibodies.
• Sometimes people test negative for SARS-CoV-2 antibodies when they have those specific antibodies. This is called a false negative.
• Talk with your healthcare professional about your test result and the type of test you took to understand what your result means.

Regardless of whether you test positive or negative, the results do not confirm whether you are able to spread the virus that causes COVID-19. Until we know more, continue to take steps to protect yourself and others.

Learn more about using antibody tests to look for past infection.