Antibody testing can determine if a person has been infected with COVID-19. B.C. is beginning to use antibody testing for limited clinical and research uses and select outbreak investigations.
: December 2, 2020 at 1:30 PM
When you are exposed to a new virus, your immune system creates proteins called antibodies to help protect you from infection. It may take your body weeks to start making the antibodies the first time it has a virus. These antibodies can be made in large numbers if your body is exposed to the same virus again, which may help your body to defend itself against infection.
Because COVID-19 is a new disease, we don’t yet know if the antibodies you create can protect you from a future infection, or for how long this protection might last.
An antibody test, also known as a serology test, looks for specific antibodies in your blood. This test is useful because it shows if you have had the infection in the past, even if you had only mild symptoms. This type of test is less useful for diagnosing a disease because it can take some time for your body to make enough antibodies to show if you are infected.
To find out if you have COVID-19 right now, and are potentially infectious to others, you need a different test, called a viral test. Viral tests require a swab sample to be taken from your nose or throat and generally look for the presence of genetic material from the virus. If positive, this determines that you are currently infected, and that you might be able to spread this infection to others.
Many companies have developed antibody tests for the virus that causes COVID-19. Health Canada has approved antibody tests for use in Canada. B.C. is beginning to use antibody testing for limited clinical and research uses and select outbreak investigations.
You cannot yet request an antibody test from your health care provider.
Antibody testing is being used for limited clinical and research uses and select outbreak investigations. Health providers may use antibody testing in limited settings, such as for patients in hospital who have less common symptoms of COVID-19 but need to have their COVID-19 infection confirmed to help direct their medical care. Health care providers and public health will work together to determine when antibody tests should be used.
Researchers in B.C. and Canada are conducting studies to try to understand whether people with antibodies to COVID-19 can get re-infected or can infect others. They are also looking at how many people have been infected with COVID-19 at a community level.
If you or someone you know has been tested for COVID-19 antibodies, here are some answers to some common questions about what the test results mean:
Positive: you were exposed to the COVID-19 virus and your body made antibodies against the virus.
Negative: antibodies against the COVID-19 virus were not found in your blood.
Inconclusive: your test result does not tell us if you have or do not have antibodies against the COVID-19 virus. This could be because you were infected with the COVID-19 virus but your body did not make a lot of antibodies or because there was a problem with the test.
You don’t need to do anything. A positive result tells you about an infection that happened in the past. It does not mean you are currently infected. If you have symptoms and think that you have an infection now, please go to a test centre to get a swab for COVID-19.
From our experience with the antibody tests so far, positive results are correct approximately 95% of the time (95 out of 100 results are correct). Negative results are correct approximately 99% of the time (99 out of 100 results are correct).
No laboratory test is perfect, but the BCCDC Public Health Laboratory is testing samples using a combination of different tests to try to improve accuracy.
We don’t currently know much about the benefits of having antibodies to COVID-19. We are not sure for how long the antibodies last or if they provide protection against future COVID-19 infections. More research is being done around the world, including B.C., to try to answer these questions.
Even if you have antibodies to COVID-19, we don’t yet know if you are protected from being infected again. Therefore, you should still follow all recommendations from Public Health on how to keep yourself and others safe.
We don’t know yet whether you can get COVID-19 again if you have antibodies. For some infections, having antibodies protects people from getting the infection again. For other infections, it doesn’t.
We don’t have recommendations for getting tested for COVID-19 antibodies on a regular basis.
Some people in a household can get sick while others do not. This is because some people are more likely to be infected, because of how much virus they were exposed to, their age or if they have any other health problems.
Also, people who are infected make different amounts of antibodies. If a person only makes a very small amount of antibodies, the test may not be able to measure it.
We don’t know how well the antibody test works for children, as most studies on antibody tests have been done in adults. Research is currently underway to understand COVID-19 antibodies in young children. In the future, if the test works well, young children may also be able to get tested.
In general, elderly people may be less likely to produce high amounts of antibodies because their bodies don’t respond to infections as actively as younger adults. This might also be true for COVID-19 antibodies.
BCCDC Public Health Laboratory currently takes blood from a vein for COVID-19 antibody testing.
The accuracy of finger poke tests has not been shown to be as accurate as laboratory-based tests, so far. Dried blood spot tests and saliva-based antibody tests are being studied.
Different people produce different amounts of antibody.
If you had a positive result from the swab test but your antibody test is now negative, this may be because you did not produce a lot of antibodies to the infection. This does not mean that your nose swab test result was wrong.
If you had a negative result from the swab test but your antibody test is now positive, the swab test may have been done when the virus was not present in your nose or the nose swab did not get a good sample, so the virus was not detected. The antibody test result shows that you were exposed to the virus and your body made antibodies. It does not tell you about when exactly you were infected or how the virus has impacted you.
Download a PDF version of the FAQs about antibody test results table.