What is a COVID-19 antibody test?

There is still a lot we don’t know about COVID-19 including how much immunity a person will develop after they have the virus.

Serology or antibody tests may be able to tell if you have been infected with the virus that causes COVID-19. Your body makes antibodies when it fights an infection. Antibody tests find antibodies in your blood. Antibody tests tell you if your immune system responded to the infection. Antibodies in your blood mean at one time you were exposed to COVID-19. An antibody test is done by taking a sample of blood. Your blood can be analyzed for two kinds of antibodies:

  • IgM antibodies which develop early in an infection
  • IgG antibodies which are more likely to show up later in the infection or after you’ve recovered from the infection

An antibody test is different from the test in which a healthcare worker uses a nasal swab to collect a sample of secretions from the uppermost part of your throat, behind your nose. This test is called a PCR test. A PCR test is used to diagnose someone with COVID-19. It tells you if you are sick with COVID-19 right now.

Can an antibody test tell me if I have COVID-19 or if I am immune to COVID-19?

Because there are few scientific studies about how accurate COVID-19 antibody tests are, the results of antibody tests should not be used to know if you have COVID-19 or if you are immune to it. Right now, we don’t know if people who have recovered from COVID-19 or who have antibodies for it are immune and protected from getting COVID-19 again.

Current COVID-19 antibody tests are best used for scientific research.

When should an antibody test be done? 

It takes about two 7-10 days for COVID-19-related IgG antibodies to be detected in the blood of someone who is infected with the virus that causes COVID-19. Testing people who are not sick yet or who are very early in their infection can result in large numbers of false negative test results because they have not yet developed antibodies to the virus. A false negative test result means someone tested negative for COVID-19 but they actually have the disease. If you want to get an antibody test, you should wait at least 2 weeks after you had symptoms of COVID-19 or were in close contact with someone who tested positive for COVID-19.

What antibody tests should be used?

Antibody tests can be done by venous blood draw or a finger-prick. Antibody tests are unreliable with a small blood sample so venous blood draw is recommended over finger-prick tests. We don’t know how accurate finger-prick COVID-19 antibody tests are yet.

For both types of tests, it is best to use one that has been validated by a laboratory to the standards of state or federal regulatory bodies. Tests that have Emergency Use Authorization (EUA) status by the Food and Drug Administration (FDA) are preferred over tests simply registered with the FDA for sale in the United States. An EUA means the test has been independently verified by the FDA.

As of April 26, 2020, only four companies had received EUAs from the FDA for antibody tests but 107 other companies were selling antibody tests. An up-to-date list of companies with EUAs by test type can be found at https://www.fda.gov/medical-devices/emergency-situations-medical-devices/emergency-use-authorizations#covid19ivd.

What does a positive antibody test result mean?

If an antibody test is positive and shows antibodies are in your blood, you were likely infected with COVID-19 and your immune system has responded. This does not guarantee you have immunity to the virus.

We don’t know how long COVID-19 antibodies will be present in the body or if they protect you from getting COVID-19 again. Because of this, it is important to still practice social distancing.

If you do get sick with symptoms of COVID-19 (like a fever, cough, shortness of breath, muscle aches, sore throat, or a decrease in your sense of smell or taste), you may need to be tested for COVID-19 with a PCR test. A PCR test is done by a healthcare worker who uses a nasal swab to collect a sample of secretions from the uppermost part of your throat, behind your nose. Call a healthcare provider or visit https://coronavirus.utah.gov/testing-locations/.

What does a negative antibody test result mean?

If an antibody test is negative and shows no antibodies are in your blood, you were likely not infected with COVID-19, you may have been tested early in your infection, or your body has not made enough antibodies to be detected by the test. Because of this, it is important to still practice social distancing.

It takes about 7-10 days for COVID-19-related IgG antibodies to be detected in the blood of someone who is infected with the virus that causes COVID-19. Testing people who are not sick yet or who are very early in their infection can result in large numbers of false negative test results because they have not yet developed antibodies to the virus. This means, you could still be infected with COVID-19 even if your test result is negative, especially if you have been in contact with someone who tested positive for COVID-19 or you have symptoms of it.

If you get sick with symptoms of COVID-19 (like a fever, cough, shortness of breath, muscle aches, sore throat, or a decrease in your sense of smell or taste), you may need to be tested for COVID-19 with a PCR test. A PCR test is done by a healthcare worker who uses a nasal swab to collect a sample of secretions from the uppermost part of your throat, behind your nose. Call a healthcare provider or visit https://coronavirus.utah.gov/testing-locations/.

Should antibody testing be used by employers to know if they can reopen their businesses?

Since we don’t know at this time if antibodies provide immunity against COVID-19, employers should not require their employees to have a positive antibody test in order to come back to work or reopen their business.

Where can I be tested?

Please contact your healthcare provider for more information on local testing.