You’ve probably heard a lot about antibodies and antibody tests as parts of the country start re-opening to the public. Dr. Rossana Rosa, infectious disease specialist, answers top questions about antibodies function, how they help our bodies and the current state of antibody testing.
What Are Antibodies?
Antibodies are substances your body produces in response to an infection. They help fight the infection off to make you well again.
Do Antibodies Truly Protect You?
In general, yes. But that protection can be partial, which would mean symptoms would be milder the next time you get an infection, or full, meaning you don’t get infected again. In terms of COVID-19 antibodies, we don’t know which type of protection is developed yet or how long that protection lasts.
What are Antibody Tests?
Antibody tests are also called serology tests. Serology tests require blood samples that are then submitted to a laboratory. The test tries to detect if you have developed COVID-19 antibodies against the virus. It doesn’t look for the virus itself, rather it measures if your body mounted a response against the virus. Serology tests are different from nasal swab tests, which try to detect the actual virus within your body based on positive results.
Are Antibody Tests Reliable?
It depends on several issues, such as the brand of test you receive, the actual community levels of infection (prevalence) and the timing from the onset of symptoms.
There is not just one antibody test, rather different companies make similar versions of the same test. Think of pregnancy tests, there isn’t just one brand, there are a lot of them. So far, very few companies have had tests cleared by the FDA. To be approved by the FDA, a company must submit information regarding the performance of their test under lab conditions. Then, the FDA decides if that information is good enough to grant approval.
Now, the other important component is the actual prevalence of infection. You may hear that a test has 95 percent sensitivity and specificity. In general, that sounds very good, but if a disease has a low prevalence in the community, then you can expect a lot of people will actually have “false positives,” meaning they are told they had the infection but actually did not.
Furthermore, many of the current tests cross-react with the four other coronaviruses that cause the common cold. This means you could test positive for COVID-19, and it is actually detecting an infection from some other coronavirus rather than the virus we’re currently concerned about.
When is the Best Time to Take an Antibody Test?
The best time to take a serology test is two weeks after the onset of symptoms. As of now, these tests are more reliable if you test negative, meaning you have NOT had an infection.
Who Should Get a Coronavirus Antibody Test?
The truth is, experts are still trying to figure out who should get antibody tests. They might be helpful to more confidently exclude infection in someone two weeks out from the onset of symptoms and negative nasal swab test results. They might also be useful to determine infection for people who think they might have had COVID-19 but couldn’t get a nasal swab.
For more information on COVID-19, please visit our coronavirus resources page.