Sonya Addison, MD, is board certified in Internal Medicine, Diabetes, Endocrinology, and Metabolism, and holds a certification by the American Society of Hypertension. She currently practices Endocrinology at Boone Medical Group Diabetes and Endocrinology in Columbia, Mo. This column is for educational and entertainment purposes, and is not meant to replace the advice of your personal medical team.

As expected, most of us are excited about the ability to determine if we’ve had COVID-19. We finally have a test that can tell us this. Right? The answer is a resounding “maybe.””

Coronavirus continues to dominate our thoughts, lives, and scientific research. Information still comes at us faster than we can process it. We now know that many infected with the novel coronavirus have no symptoms at all. How do we know if we’ve had the virus?

Multiple antibody tests are now available. Who should be tested?

What is an antibody and how do we get them? An antibody is a protein that is made by plasma cells (which are types of blood cells) in response to a foreign invader. Our immune system kicks into action when we are infected with a virus or bacterium. The infectious organism has proteins or other substances on the surface, called antigens. Through a very complex system, our body “learns” these antigens, and then can make an antibody that is very specific to the invader. The next time we come into contact with that particular infection, the now formed antibodies can attach to the organism, killing or disabling it quickly. 

Antibodies are important. They keep us from getting many infections a second time. Some will keep us safe for a short time while others give us life-long protection against the infection. Vaccines work by introducing an antigen and allowing our body to make the antibodies. The infectious part of the virus or bacteria has been removed or altered so we do not get the disease, but can still make the antibodies.  Some vaccines only require one or two doses (chicken pox), while others need to be given repeatedly through life (tetanus). 

As expected, most of us are excited about the ability to determine if we’ve had COVID-19. We finally have a test that can tell us this. Right? The answer is a resounding “maybe.”

Despite the vast research regarding COVID-19, we still don’t know everything about it. While it feels like years, remember that it has only been around for a few months. 

We don’t yet know if a prior COVID-19 infection, thus having antibodies, protects us for life, a few months, or at all. Therefore, knowing if you’ve had it doesn’t give us any predictions about future immunity. Each illness can also cause the body to produce several different antibodies to that organism. Researchers are still not sure which coronavirus antibody might be the “best” one to predict prior infection. 

Current antibody tests are not very accurate. It takes the body time to make these antibodies after having an infection. The test might be falsely negative if an active infection is present or if it has only been a couple of weeks after recovery. People who had a very mild or asymptomatic infection may have a false negative result, as well. The body may make low amounts of antibody (or none at all) if the infection is mild. More simply put, the body didn’t see the infection as much of a threat (because it was mild), so the antibody response is weak.

An antibody test should not be used to test for a current infection for the reasons above. If a current infection is suspected, then a test for novel coronavirus genetic material is needed. 

Sometimes the test can be positive when a person hasn’t had COVID-19. Coronaviruses are a large family of different viral strains. Many cause the common cold. Most of us have been exposed to these other strains over the years, and have antibodies against them. The COVID-19 antibody test may pick up on those antibodies, and because some of them are the very similar to the COVID-19 antibodies, the test will come back as positive.

I’ve had patients ask for an antibody test to see if it is safe for them to go back to work. It is not recommended that these tests be use for this. Again, this is because we don’t know if having a past COVID-19 infection will protect you from getting it again, and because they aren’t very accurate yet.

With this information, why would we ever test for antibodies? One reason is to see if a person would be a candidate for donating convalescent plasma. When high levels of COVID-19 fighting antibodies are present in the plasma, then it could be used as a treatment for someone who is ill with an active infection.

Antibody tests will also be a very valuable tool for epidemiologic studies to learn more about this coronavirus. As they become more accurate, we will learn about transmission patterns, how many people were infected without knowing it, and true hospitalization and death rates. This extremely valuable information will help us when the (gulp) next pandemic arises. 

Sonya Addison, MD, is board certified in Internal Medicine, Diabetes, Endocrinology, and Metabolism, and holds a certification by the American Society of Hypertension. She currently practices Endocrinology at Boone Medical Group Diabetes and Endocrinology in Columbia, Mo.  This column is for educational and entertainment purposes, and is not meant to replace the advice of your personal medical team.