COVID-19 antibody testing

Overview

COVID-19 antibody testing is a blood test. The test can provide information about how your body reacted to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 is the name of the virus that causes coronavirus disease 2019 (COVID-19). It also can show how your body reacted to COVID-19 vaccines. Antibody testing also is known as serology testing. A negative serology test means no antibodies were detected in your blood.

An antibody test can't find out whether you're currently infected with the COVID-19 virus. And antibody tests shouldn't be used to see if you're protected from COVID-19. An antibody test also won't tell you if you need a vaccine.

Your immune system makes antibodies in response to an infection. Your immune system involves a complex network of cells, organs and tissues. This system identifies foreign substances in your body. And it helps clear out infections and diseases. After infection with the COVID-19 virus or a COVID-19 vaccine, your body can take 2 to 3 weeks to make enough antibodies to be found in an antibody test. So it's important that you're not tested too soon.

Antibodies may be remain in your blood for many months. These antibodies are thought to give some form of immunity to the COVID-19 virus. But there's currently not enough evidence to know how long the antibodies last. More research also is needed to know how much past infection with the virus helps protect you from getting another infection. Studies are ongoing to learn more about COVID-19 antibodies as well as other parts of the immune system.

Antibody tests may find some types of antibodies related to the COVID-19 virus:

• Binding antibodies. These widely available antibody tests find whether you've made any antibodies in response to a COVID-19 infection. But they don't show how widespread or effective your immune response is.
• Neutralizing antibodies. Used mostly for research, this test finds a subgroup of antibodies that prevent the virus from infecting your cells. This test can be done after you test positive for binding antibodies. It's another step toward finding out how well your antibodies are blocking the virus to help protect you from another COVID-19 infection.

Why it's done

Antibody testing for COVID-19 may be done if:

• You had symptoms of COVID-19 in the past but weren't tested.
• You had a serious reaction to the first shot of a COVID-19 vaccine.
• You've had a COVID-19 infection in the past and want to donate plasma. Plasma is a part of your blood that contains antibodies that can help treat others who have severe cases of COVID-19.

If a child is sick and the health care provider thinks it's multisystem inflammatory syndrome in children (MIS-C), the doctor may order antibody testing. This test can help diagnose MIS-C. Many children with MIS-C have antibodies to the virus that causes COVID-19, showing past infection with the coronavirus.

If you're interested in having a COVID-19 antibody test, contact your care provider or your local health department. Whether or not you're eligible for testing may depend on the availability of tests in your area and local or state health department guidelines.

Risks

Results of COVID-19 antibody tests may not always be accurate. Results may not be accurate if the test was done too soon after infection or the test quality is uncertain. At the start of the pandemic, there was a rush to get antibody tests on the market. Now the U.S. Food and Drug Administration posts data online about the performance of some antibody tests. The results may vary based on which strain of the virus is spreading in your area.

COVID-19 antibody testing could lead to false-positive or false-negative test results:

• False-positive result. The test result is positive. But you actually don't have antibodies at the time of the test. A false-positive result could give you a false sense of security that you're protected from getting another COVID-19 infection. Even with a true positive result, your personal level of immunity may vary.
• False-negative result. You have antibodies to the COVID-19 virus. But the test doesn't find them. Or you're tested too soon after infection and your body hasn't had time to make antibodies.

How you prepare

Your doctor or testing center will tell you where to go for testing and how the test will be done. Ask if you, and anyone who comes with you, need to wear a face mask to and from the testing center.

What you can expect

To do a COVID-19 antibody test, typically a member of your health care team takes a blood sample. It's taken by a finger prick or by drawing blood from a vein in your arm. Then the sample goes to a lab for testing to find out whether you've developed antibodies against the COVID-19 virus.

COVID-19 antibody test results may be ready the same day as your test at some sites. Other places may have to send test samples out to a lab for testing. So results may not be ready for a few days.

Results

COVID-19 antibody test results could be:

• Positive. A positive test means you have COVID-19 antibodies in your blood. A positive result shows past infection with the virus. It's possible to have a positive test result even if you've never had any COVID-19 symptoms. False-positive test results can happen. It may be that the test found antibodies to a coronavirus closely related to the COVID-19 virus. Or the test quality may have been flawed.
• Negative. A negative test means that you have no COVID-19 antibodies. So you probably were not infected with the COVID-19 virus in the past. Because it takes time for antibodies to be made, false-negative test results can happen if the blood sample is collected too soon after your infection started. In some cases, the test may be flawed.

People who have had COVID-19 or tested positive for antibodies shouldn't assume they're protected from getting a COVID-19 infection again. Reinfection is known to occur. Researchers are trying to find out how much protection antibodies provide against the COVID-19 virus, what the level of protection is and how long immunity may last.

Until there is more information, even if your test results show that you have COVID-19 antibodies, keep taking steps to avoid the risk of spreading the virus. This includes getting vaccinated, avoiding close contact with anyone who is sick or has symptoms, and washing your hands often.