Who Should Get An Antibody Test & What Can Results Tell Us?

May 11, 2020

By Michael Bohl, MD, MPH
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Now that the rate of COVID-19 infection is taking a dip in most regions, everyone’s talking about antibodies and antibody testing. In bigger cities like New York, antibody test results are seeing staggering figures: one in five people tested so far have tested positive for antibodies. But what exactly are antibody tests and what can they tell us? Who should get antibody tests and how easy are they to come by?

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There are two main types of COVID-19 tests available: nucleic acid amplification tests (NAATs) and serology tests (antibody tests). NAATs are the tests that are used to diagnose active cases of COVID-19. That means if you’re sick and meet the guidelines for COVID-19 testing, the test you get will be a NAAT. NAATs directly look for the virus that causes COVID-19 by seeing if any of the virus’s genetic material (its RNA) is present.

Serology tests, on the other hand, are used to see if you’ve been infected with the COVID-19 virus in the past. The U.S. Food and Drug Administration (FDA) has granted emergency use authorization for these tests and they are slowly becoming more available for the public. Unlike NAATs, serology tests do not directly look for the COVID-19 virus. Instead, serology tests look for certain antibodies to the virus.

Antibodies are small proteins in the blood that function as part of the immune system. Whenever you become sick with an infection, your body creates antibodies to fight off whatever is infecting you. You only develop antibodies to something if you have been exposed to it in the past — that’s what makes serology tests good for determining whether you have had a disease in the past. If you’ve ever had an HIV test, a hepatitis test, or you’ve had titers drawn, you’ve had a serology test before.

Who Should Get an Antibody Test?

Currently, there aren’t any guidelines regarding who should get an antibody test and who shouldn’t. An important thing to note about antibody tests is that they don’t work immediately because the body doesn’t make antibodies immediately. The Centers for Disease Control and Prevention (CDC) points out that it can take the body 1 to 3 weeks to make antibodies to COVID-19. A study found that the median time from when symptoms start to when COVID-19 antibodies are detectable in the blood is 12 to 14 days (depending on the type of antibody). This is why antibody tests are not great at diagnosing an active infection.

So, when determining if the test is right for you, you should start out by asking yourself one question: How will the results impact you? Maybe you were sick earlier in the year and want to know if it was COVID-19. Or maybe you haven’t felt sick at all, but you know that many people who get the virus are asymptomatic, so you want to find out if you’ve had the virus anyway.

In many cases, antibody tests can be very useful. For example, if you have measles antibodies, it means you are immune to the measles (except in very rare circumstances). Antibody tests can also help researchers and the government understand the pandemic better. By knowing how many people have already had the infection, more can be learned about how the virus spreads and how often cases are asymptomatic. This can be useful information when planning for the future.

However, there are two main things we still don’t know about COVID-19 antibody tests that makes their results hard to interpret: how accurate they are and what it means if you do actually have the antibodies.

How accurate they are: Antibody tests for COVID-19 are new. This means we do not yet know how good they are at detecting the relevant antibodies and how frequently the results are incorrect (a.k.a. how frequently the results are false positive or false negative). False negatives are especially likely if you were only exposed to the virus in the past 1–3 weeks, since your body may not have had time to develop antibodies yet.

If you do have the antibodies: If you find out you do have the antibodies, you may think this is a good sign. For many diseases, the presence of antibodies means you can’t get the disease again. Unfortunately, we don’t yet know if having antibodies to the COVID-19 virus offers any sort of protection. In other words, we don’t know if it’s possible to get COVID-19 more than once. It’s possible that the antibodies provide lifelong immunity, or that they only provide immunity for a short amount of time (weeks to years), or that they provide no immunity at all. Research is currently underway to figure this out — but it will take time. Plasma donation is one way people with antibodies can help researchers. Researchers can look at these antibodies to see which specific ones are more effective at combating the virus and in what amounts they may be protective.

How to Get Tested & What The Test Entails

Keep in mind antibody tests might not be widely available where you live yet. Before going anywhere, call your healthcare provider or local lab ahead of time to see if they are offering the serology tests. If so, ask if they are offering them to everybody or if there are specific criteria regarding who can get tested.

Since there are so many different antibody tests available, your exact experience will depend on the test you get. Antibody tests often rely on a blood sample (either a blood draw or a fingerstick) and results are available anywhere between a few minutes later to a few days later.

When you do get your results, keep these two things in mind: 1) Your test results may not be accurate, and 2) Even if you do have antibodies, you may not be protected from getting sick again. Because of this, regardless of your results (and until we better understand the usefulness of antibody tests), you should continue behaving as though you are still at risk of getting and/or spreading COVID-19. Continue practicing social distancing, continue washing your hands frequently, and wear a cloth face covering in public.

Related: 

Why Do False Negatives Happen In COVID-19 Tests?

The Harmful Effects of Staying Home for Too Long, According to New Research

How to Manage Mental Health, Grief & Addiction During COVID-19

Article written by Michael Bohl, MD, MPH