Serologic (Antibody) Testing

Antibody blood tests, also called serologic tests, check your blood by looking for antibodies, which show if you had a previous infection with the virus. Depending on when someone was infected and the timing of the test, the test may not find antibodies in someone with a current COVID-19 infection. Antibodies are proteins that help fight off germs. Serologic tests should not be used as the only way to diagnose someone as being currently sick with COVID-19.
Serologic tests are slowly becoming available through healthcare providers.

How to get a serologic test

Check with your healthcare provider to see if they offer serologic (antibody) tests.

If you test positive:

A positive test result shows you have antibodies that likely resulted from an infection with SARS-CoV-2, or possibly a related coronavirus.
It’s unclear if those antibodies can provide protection (immunity) against getting infected again. This means that we do not know at this time if antibodies make you immune to the virus.
If you have no symptoms, you likely do not have an active infection and no additional follow-up is needed.
If you have symptoms and meet other guidelines for testing, you would need another type of test called a nucleic acid test. This test uses respiratory samples, such as a swab from inside your nose, to confirm COVID-19. A serologic test alone cannot tell if you definitely have COVID-19.
It’s possible you might test positive for antibodies and you might not have or have ever had symptoms of COVID-19. This is known as having an asymptomatic infection, or an infection without symptoms.

If you test negative:

If you test negative for COVID-19 antibodies, you probably did not have a previous infection that has gotten better. However, you could have a current infection. It’s possible you could still get sick if you have been exposed to the virus recently, since antibodies don’t show up for 1 to 3 weeks after infection.
Some people may take even longer to develop antibodies, and some people may not develop antibodies.
If you have symptoms and meet other guidelines for testing, you would need another type of test called a nucleic acid test. This test uses respiratory samples, such as a swab from inside your nose, to confirm COVID-19. A serologic test alone cannot tell if you definitely have COVID-19.

Know How to Protect Yourself and Others

CDC’s Work in Serology Testing

CDC is evaluating commercial tests

CDC is evaluating the performance of commercially manufactured serologic tests in collaboration with other government agencies. FDA has authorized emergency use of several serologic tests.

For more information:

CDC is conducting serologic surveillance

CDC is looking at data from serology tests to estimate the total number of people who have been infected with SARS-CoV-2 in the United States. CDC is also using serologic testing to learn more about how the body’s immune system responds to the virus and to explore how the virus spreads among people exposed to it. The information CDC is looking at comes from many groups, including blood donors and household contacts of people who had symptoms and were diagnosed with COVID-19.

CDC is supporting state, local, tribal and territorial laboratory capacity.



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