Everything to Know About COVID-19 Antibody Testing

Ashley Abramson

If you had symptoms like a fever, cough, shortness of breath, and fatigue as in the early days of the pandemic in March and April, your doctor may have thought you were infected with the SARS-CoV-2, the virus that causes COVID-19 (though a CDC report released earlier this month suggests that COVID-19 cases were in “limited spread” within the U.S. as early as January). However, as Gigi Gronvall, an immunologist and senior scholar at the Johns Hopkins Center for Health Security explains, COVID-19 tests weren’t readily available early on in the pandemic, so for many, most of those whose symptoms have since subsided (unlike those who are still battling the virus after months), and are unable to confirm whether or not they had COVID-19. But now, there's another option that could provide answers.

Patients who presented with symptoms but were unable to be tested and get a diagnosis may now look to antibody tests to find out if their illness was actually COVID-19. But it’s not so cut and dry as it may seem. While antibody tests can provide some peace of mind, the results should be taken with a grain of salt, as research about what it means to have SARS-CoV-2 antibodies is ongoing, and there are multiple tests on the market with varying levels of accuracy. If you’re thinking about getting a COVID-19 antibody test, here’s what you need to know.

What is antibody testing, and how does it work?

According to Amy Karger, an associate professor of laboratory medicine and pathology at the University of Minnesota Medical School, testing for antibodies — or, proteins the body produces to fight off antigens — can confirm whether a person had an infection in the past.

“It’s a way to tell if [your body] mounted an immune response to an infectious disease,” she explains. “For COVID-19, you’re checking if a person has those antibodies, which is a sign you had an immune response to COVID-19.”

Karger says antibody testing typically occurs by obtaining a blood sample. “The tests all have proteins that are from the virus,” she tells Allure. “If the antibodies in the blood bind to those proteins from the test, you’ll get a positive signal. It’s basically trying to figure out if you have those antibodies that specifically bind to the virus, and that indicates that you had an infection, either current or past.”

Usually, Karger explains, antibodies don’t appear in the body until one to two weeks after symptoms start, and they remain in the body for an undetermined period of time to fight off infection. Asymptomatic people, or those who may have been infected but don’t present with symptoms, can also have antibodies. “Every disease is different in terms of how long the antibodies are detectable after the initial infection,” she explains. “Someone could have the antibodies without ever having symptoms.”

What does antibody testing tell us about COVID-19 immunity?

Angela Rasmussen, an associate research scientist and virologist at the Columbia University Public Health’s Center for Infection and Immunity, says the presence of antibodies may indicate some level of immunity to an infection. But the presence of SARS-CoV-19 antibodies doesn’t mean a person will never get COVID-19 again.

Several early studies suggest that people who were actively sick with COVID-19 develop protective antibodies. But research is still ongoing, and doctors haven’t been able to follow patients long enough to know how long antibodies last. One recent study in China suggests immunity may only last for only two to three months, including for people who were infected but showed no symptoms.

“It does look like people develop some kind of immunity to [COVID-19], but we don’t know how long it lasts or how complete it is,” Ramussen says.

Similarly, people could have SARS-CoV-19 antibodies and be “immune” in the sense they won’t have COVID-19 symptoms again, but Rasmussen says people could still be infected and transmit the virus to others.

That’s why even if you have antibodies, it’s important not to change your behavior. “If I found out I was antibody positive, I would still practice social distancing, wearing a mask in public, avoiding crowds, taking all the same precautions I’m taking right now,” she says. “Until we know more until the type of immune protection you get, people should still continue to take the same precautions to protect the community.”

How does testing for antibodies differ from testing for COVID-19?

Thomas Briese, an associate professor of epidemiology at the Columbia University Medical Center, says the COVID-19 test is a diagnostic test that detects the SARS-CoV-2 virus. It usually takes place in the timeframe when a person is actively sick. “You do a swab and then analyze whether you see the genetic material of the virus, which then indicates the presence of the virus,” he tells Allure.

The antibody test, on the other hand, doesn’t diagnose COVID-19; instead, it shows people they’ve been infected at some point — which could indicate a current or past infection. Testing for antibodies isn’t meant to diagnose an active COVID-19 infection, as Briese explains it takes around a week after symptoms surface for antibodies to develop. However, someone with COVID-19 may still feel sick and have antibodies.

If you were exposed to someone who has COVID-19, or you’re feeling sick, Rasmussen says it’s important to call your health care provider to get tested for the virus. If you think you had COVID-19 in the past, talk to your provider about the antibody test.

What is the FDA’s stance on antibody tests?

According to Gronvall, early on the pandemic, the FDA focused on COVID-19 tests instead of antibody tests. “The FDA took a hands-off approach and let a lot of companies move into the market to provide them,” she says. “The antibody tests didn’t have to be independently validated, and the accuracy claims came from the developers themselves, so a lot of the tests aren’t good.”

As of May, she says, the FDA tightened the reins to validate antibody tests, but it’s not always clear to the consumer which tests are the most accurate. Rasmussen tells Allure that some antibody tests currently on the market have a high rate of false positives as well as false negatives. “False positives are a worse problem, in my opinion, because you think you’ve had COVID and you’re protected from it, but you actually just had a false test result,” she says. “That could put a lot of people in danger.”

Rasmussen says there are more than a hundred tests on the market total, but not all of those tests are reliable. As of June 29, when the FDA last updated its site, the FDA has reviewed and authorized 24 antibody tests. The list of those tests is available here on their site.

If you plan to undergo antibody testing, Rasmussen recommends finding out how reliable the specific test is beforehand. The package insert on any antibody test will list how specific and sensitive the test is, so you can either ask your doctor for those details or look up those insert details online.

So far, Karger says there are no at-home antibody testing options available to consumers — there are researchers exploring ways to collect samples from home, but this would be limited to individuals who are enrolled as part of a research study. “This is a developing area of research, but not ready for primetime yet,” she says.

Should I get an antibody test?

Even though a positive antibody test doesn’t guarantee immunity and shouldn’t change a person’s social distancing behaviors, Karger and Rasmussen recommend antibody tests, as they can still be beneficial for several reasons.

“Antibody testing is helpful on an individual level because it can help us understand how the virus is spreading within households,” says Rasmussen. “It also will help patients better report their own medical status, which is important for their providers to be informed while providing care.”

Beyond helping an individual manage their health, Karger says antibody testing can also be beneficial from a public health perspective, helping medical experts understand how many people in a given population have had COVID-19.

Antibody tests, when accurate, can tell the “history” of infection in an individual. Also, Karger says not everyone has been able to get a COVID-19 diagnostic test due to shortages, long wait times, and she says there is currently no shortage of antibody tests available.

“Antibody testing provides us with more data about how this disease is spreading and who has been affected,” she tells Allure. “The more data we have, the better we can understand the virus and potentially predict rates of spread in the future as we are able to look back on past trends.”

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Originally Appeared on Allure

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