COVID-19 antibody (serology) testing: Information for patients

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Organization: Health Canada

Published: 2020-11-27

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What you should know

  • Antibody (serology) tests use a sample of your blood to check for antibodies. Your body makes antibodies after it is infected by a virus or other infectious agents.
  • It takes time for your body to make antibodies. They usually start to appear in your blood 7-10 days after your initial infection by the virus.
  • It is not known how long antibodies to the SARS-CoV-2 virus will remain present in your body after infection.
  • It is not known whether having antibodies to the SARS-CoV-2 virus will protect you from getting infected again or will help reduce how severe or how long a future COVID-19 infection may be. Regardless of your test result, you must continue to follow public health guidelines to reduce the risk of infection.

How are people tested for COVID-19

Two kinds of tests are currently available for COVID-19: tests for viral infection and antibody (serology) tests.

  • A test for viral infection detects the virus or a component of the virus and tells you if you have a current COVID-19 infection. This is done using a swab from your nose or throat, or a saliva sample.
  • An antibody (serology) test tells you if you, at some point, were exposed to the virus and had a COVID-19 infection. This test is done using a sample of your blood.

Serology tests aren't used to diagnose a current SARS-CoV-2 viral infection, since they don't detect the virus itself.

A positive antibody (serology) test means that, at some point, you were infected by the SARS-CoV-2 virus, the virus that causes COVID-19.  It can't tell how long ago you were infected or confirm that you are immune or protected from being reinfected.

What does it mean if you have a positive test result

If you have a positive serology test result, it is likely that you previously had a COVID-19 infection and that you developed an antibody response to the virus.

Receiving a positive result indicates that you have been exposed to the virus but does not necessarily mean that you are immune or protected from being reinfected.

There is also a chance that this test can give a positive result that is wrong (a false positive result). Even a very precise antibody test may produce false positive results on occasion.

If you have questions about the results of your antibody test, it is important to talk to your health care provider to help you understand.

What does it mean if you have a negative test result

If you have a negative serology test result, it likely means that antibodies to the virus that causes COVID-19 were not present in your sample.

It is possible for this test to give a negative result that is wrong (a false negative result) even if you have previously been infected with COVID-19.

You may also have a negative test result because you were tested too early, before your body had time to produce antibodies.

If you have questions about the results of your antibody test, it is important to talk to your health care provider to help you understand.

Follow public health advice to slow the spread of COVID-19

Even if you have previously had a COVID-19 infection, you must still follow public health advice and take the same actions to prevent COVID-19 as someone who has never had the infection:

  • Wash your hands often with soap and water for at least 20 seconds.
  • If soap and water aren’t available, use a hand sanitizer containing at least 60% alcohol.
  • Stay home as much as possible and if you need to leave the house, practice physical distancing (approximately 2 m).
  • Wear a non-medical mask or face covering to protect others when you can't maintain a 2 metre distance.
  • Avoid close contact with people who are sick.
  • Cough and sneeze into your sleeve and not your hands.
  • Follow the advice of your local public health authority. 

Please contact your health care provider with any questions or concerns about your test.

For more information on COVID-19: 1-833-784-4397 Canada.ca/coronavirus

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