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Do I Need to Get an Antibody Test?

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Arefa Cassoobhoy, MD, MPH - Blogs
By Arefa Cassoobhoy, MD, MPHBoard-certified internistMay 22, 2020

Do you wonder if you had COVID-19, but aren’t sure because you never were tested?

An antibody test might give you an answer.

What is an antibody test?

An antibody test, also called a serology test, is a test of your blood serum that checks for your body’s response to an infection.

An antibody is a protein produced by white blood cells in your immune system to respond to a toxin or foreign substance in the body (in this case, the SARS-CoV-2 virus that causes COVID-19). The antibody then attaches to the virus and signals to the rest of the immune system to come attack it. 

Usually your body produces a first round of antibodies within about a week of symptoms starting, and then a second round generally within 2 weeks of symptoms starting. It takes about 1-3 weeks for the antibodies to be detectable on testing. Some people may take longer to produce the antibodies. Currently, there are many different antibody tests available with varying accuracy.

This is very different from the COVID-19 viral antigen test, which is a deep nose swab or saliva test that actually looks for the SARS-CoV-2 virus to check if you are infectious now.  

Who should get an antibody test?

If you’re interested in finding out if that illness you had months ago was COVID-19, or if you haven’t had any symptoms but are wondering if you’ve already been exposed to the SARS-CoV-2 virus, you could get an antibody test now. But it’s probably worth waiting for a few months until it’s more clear which tests are performing the best.

If you have had COVID-19 in the past – or strongly suspect that you have – you may want to go ahead and get an antibody test because there is a need for donated convalescent plasma right now. That’s when the plasma portion of blood rich with antibodies from a person who’s recovered from the COVID-19 infection is given to a person very sick with the disease.

Whether you’ve had the virus or not, you may be approached at some point to be tested for research purposes. Public health officials need the data to help calculate how many people overall have had COVID-19 and understand how many people were infected but never got sick. The results may help with complicated questions ranging from when to relax social distancing, to is reinfection with COVID-19 a concern? Participating in testing is a great way to contribute to our knowledge about COVID-19.

How accurate are antibody tests?

There’s definitely a problem with false results with antibody tests right now. It’s difficult to know how much we can rely on a positive or negative test.

One issue is there aren’t that many people across the United States with antibodies to COVID-19. Even the best tests will have incorrect results when the likelihood of finding someone who was infected is small.

Another issue with some tests is cross reactivity, where the antibody test comes back positive, but we’re not sure if it’s really for the SARS-CoV-2 virus. Instead it might be positive from a past exposure to one of the 4 coronaviruses we know lead to the common cold.

To add to the confusion there are over 200 antibody tests out, but only 13 are FDA authorized for emergency use (EUA) as of May 21, 2020. The FDA is working to evaluate the various tests, but it’s taking time to process all the requests for FDA EUA status.  In the meantime, some tests are being sold inappropriately and some are just bad tests. 

Where can you get a good antibody test?

Availability of antibody tests varies from state to state – some are stricter than others about what tests are allowed to be given, and who can take the tests. Check your state’s department of public health for the latest information, and talk with your doctor about whether a test is appropriate for you.

When you do find a location offering tests, make sure the antibody test is authorized for FDA emergency use. You can check on the FDA serology test page.

If you had COVID-19 and would like to be a plasma donor you can check the FDA page Donate COVID-19 Plasma to find a resource in your area. You’ll need to be in good health, fully recovered with no symptoms from COVID-19. If your diagnosis wasn’t verified with a viral test, they will give you information about antibody test options.

What do the results of the antibody test mean?

Let me just say, interpreting the antibody tests results is complicated and not straightforward. You’ll want to talk with your doctor to understand how the results impact you. Here’s some basic info:

If your antibody test is positive and you have no symptoms of COVID-19, you likely were infected with the SARS-CoV-2 virus, especially if you had the classic COVID-19 symptoms when others in your area also were sick.

If you didn’t have obvious symptoms, the positive result could still be true because some people do have the infection without symptoms. Or, it could be a false positive from one of the related coronaviruses known for causing the common cold.

If your antibody test is negative, you probably were not infected in the past with the SARS-CoV-2 virus.

It’s important to note, a negative antibody test does not mean you don’t currently have an infection with the SARS-CoV-2 virus. You could be infectious to others, even if you don’t have symptoms. You would need the viral test to check if you are infected now.

Does a positive antibody test mean I have immunity to COVID-19?

Ideally, antibodies stick around and remember a virus, if you’re exposed to it again, the antibodies will mobilize the immune system to stop a second illness. But the SARS-CoV-2 virus is new, and while the antibodies may give some protection, we don’t know what kind of protection that will be. Research is ongoing to answer the many questions. How effective are the antibodies at fighting a second infection?  How many antibodies do you need for a successful immune response? How long will the antibodies stay with you – is it a few months or years?

If I tested positive, do I still need to social distance?

Yes. The antibody test results alone do not give you the reliable data needed to stop social distancing. I know this is frustrating, but ideally, over time doctors will fine tune using antibody test results in combination with the viral test and other health information to give you clear advice. Until then, continue to protect yourself and others with preventive measures like avoiding crowds, wearing a facemask, keeping a minimum 6-foot distance from others, and washing your hands.

 

 

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About the Author
Arefa Cassoobhoy, MD, MPH

Arefa Cassoobhoy, MD, MPH is a board-certified internal medicine doctor and a WebMD Medical Editor. She is on the team that makes sure all WebMD content is medically correct, current and understandable. She sees patients at the Women’s Wellness Clinic at the Atlanta Veterans Affairs Medical Center.

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