What does a positive antibody test mean?

Serological (antibody) tests can tell you if you previously had COVID-19. But no antibody test is perfect. There are several reasons a test might give a false positive result, meaning the test says you have antibodies to the novel coronavirus when you really don’t. The rate of false positive results varies depending upon the specific test, and there are more than 100 tests on the market now. But it could be as high as 6%.

A false positive rate of 1% might not sound that bad. But it can cause big problems if only a few people have had the disease. Let’s imagine what would happen if you tested 100 people, and only one of them had recovered from COVID-19 and developed antibodies. If the test worked perfectly, you would have one true positive antibody test. But with a 1% false positive rate, you would end up with two positive tests: one true positive, and one false positive. That means if you got a positive test, there is a 50% chance you would think you had COVID-19 antibodies when you really did not.

Even if your test result is correct, we do not yet know whether you’re immune after you recover or for how long that immunity might last. 

At this time, it’s not safe to assume that a positive antibody test means you cannot be infected with the novel coronavirus. So, to protect yourself and others, you should act as if you are not immune.

 

Last update: May 19, 202, 10:45 pm ET

Science review: ERS, JAB