What Is an Antibody Test?
An antibody test is a screening for things called antibodies in your blood. Your body makes these when it fights infection, like COVID-19. The same thing happens when you get a vaccine, like a flu shot. That’s how you build immunity to a virus.
You may also hear it called a serology test.
The antibody test isn’t checking for the virus itself. Instead, it looks to see whether your immune system — your body’s defence against illness — has responded to the infection.
How Does an Antibody Test Work?
A technician will take a bit of your blood. The test looks for one or both kinds of antibodies to SARS-CoV-2, the virus that causes COVID-19:
- IgM antibodies, which happen early in an infection
- IgG antibodies, which are more likely to show up later
Most people have IgG antibodies about 10 days after symptoms start. They usually stay in your blood long after the infection goes away, but we don’t know how long that is for the new coronavirus.
What’s the Difference Between a Coronavirus Test and an Antibody Test?
A coronavirus test, sometimes called a diagnostic test, looks for signs of active virus. It’s simpler and faster than an antibody test. But it tells you only if you have the virus in your body at the moment when you’re tested.
An antibody test shows that you had the virus at some point in the past. It could be gone, or you could still be contagious.
Why Do We Need Antibody Testing?
You could have SARS-CoV-2 and not know it. Not everyone who gets it has symptoms. Experts hope antibody tests can give health officials a better idea of how common the virus is.
Once scientists know who has had the virus, they can find out how sick it makes most people. And they can study what happens if people who’ve had it come into contact with it again. Along with other scientific information, this can help researchers understand who might be immune to the virus.
The hope is that people with antibodies to COVID-19 can safely get back to work, and normal life, quicker.
These tests may also help with an experimental treatment for COVID-19 called convalescent plasma. Plasma is the liquid part of your blood.
Researchers are studying how antibodies in plasma donated by people who’ve recovered from COVID-19 might help those who are ill with the virus. One theory is that this plasma may help sick people get better faster. But more research is needed…
Who Should Get an Antibody Test?
If you think you might have come into contact with the coronavirus, or if you’ve tested positive for COVID-19 and have fully recovered, you can probably get tested for antibodies.
What Do the Results Mean for You?
If you test positive for SARS-CoV-2 antibodies, it probably means you’ve had the virus. It’s also possible to get a “false positive” if you have antibodies but had a different kind of coronavirus.
A positive result might mean you have some immunity to the coronavirus. It’s too early to know how strong it is or how long it might last.
A negative result means you haven’t come into contact with the virus or you haven’t had it long enough to make antibodies. You could also have been exposed and not have antibodies. This is called a false negative.
No matter the result, if you don’t have symptoms, you don’t need follow-up. But if you do, you might have a diagnostic test to look for signs of active virus.
Because there’s a chance that test results can be wrong and because there’s so much we don’t know about the virus, it’s important to keep following official safety guidelines after your test. Stay home as much as you can, wear a cloth face mask when you’re in public, and wash your hands often.
What do your results mean?
If you test positive
- A positive test result shows you may have antibodies from an infection with the virus that causes COVID-19
- We do not know yet if having antibodies to the virus that causes COVID-19 can protect someone from getting infected again or, if they do, how long this protection might last.
- You should continue to protect yourself and others since it’s possible you could get infected with the virus again.
- 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 criteria for testing, you would need another type of test called a viral test via nasal swap. This test identifies the virus that causes COVID-19.
- You might test positive for antibodies even if you never had symptoms of COVID-19. This can happen if you had an infection without symptoms (also called asymptomatic infection).
If you test negative
- You may not have had COVID-19 before.
- You could still have a current infection.
- The test may be negative because it typically takes 1 to 3 weeks after infection to develop antibodies. It’s possible you could still get sick if you have been exposed to the virus recently. This means you could still spread the virus.
- Some people may take even longer to develop antibodies, and some people may not develop antibodies.
- If you have symptoms or develop symptoms after the antibody test and you meet other criteria for testing, you would need another type of test called a viral test via nasal swap.
Regardless of whether you test positive or negative, the results do not confirm whether or not you are able to spread the virus that causes COVID-19. Until we know more, continue to take steps to protect yourself and others.