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COVID-19 Antibody Testing

The Medical Student Minute for the Georgia Rural Health Innovation Center

Welcome to the Medical Student Minute! We are so glad you’re here. Through this forum, Mercer School of Medicine students will provide informational updates on some hot topics in the world of public health, medicine, and rural health. This is not medical advice. Have a topic you’d like us to cover? Submit it for consideration to Stephanie Basey: [email protected].

COVID-19 Antibody Testing:  What is it? Do I need it?

Let’s start by talking about the immune system. Our immune system acts as an army against invading intruders like viruses (ex: SARS-CoV-2 which causes COVID-19/the novel coronavirus), harmful bacteria (Ex: E.coli which can cause food poisoning), fungus (ex: Candida albicans which can cause yeast infections) or any harmful invader or pathogen the body can recognize. The immune system “army” uses several different ways to attack, depending on what pathogen is present. With viruses, it is quite complicated! But, in short, we have these amazing immune system cells that move around the body searching for cells that have been infected with the virus; when these infected cells are found, these immune system cells help to eliminate the infection. While this is happening, another part of our immune system is roaming the body searching for cells that appear foreign. When a cell is found that seems unusual or like it might not belong in the body, that cell is marked and then presented to a B cell lymphocyte. The B cell lymphocyte then created an antibody to that foreign pathogen. This antibody is basically a form of cell memory and allows the body a way to defeat the virus faster if introduced again. It’s important because it allows our army to have a battle plan rather than having to deal with a sneak attack of an intruder. If I lost you there, as a recap, antibodies help your body recognize the virus and create a way to tag and destroy that same virus faster the next time it enters your body! This is an amazing process, and vaccines are a way science has advanced to help our body do this faster, and without having to suffer through the dangerous or deadly illness to achieve immunity or develop these antibodies.

Per the US Food and Drug Administration (FDA), there are two types of tests currently available for the virus that causes COVID-19.  Molecular tests are being used to diagnose patients with the disease by detecting the virus’s genetic material, and antibody or serology tests which detect those little antibodies we learned about earlier. These antibody tests are looking for the body’s immune response to the virus. With any healthcare test or drug used in the US, the FDA usually has a rigorous process in place to ensure only the best products are allowed on the market. After all, you don’t want a COVID-19 test that accurately detects the virus only 60% of the time, right? During public health emergencies, many of those normal processes and restrictions to bring a test to use a given population have been removed. Tests that have potentially been through less rigorous analyses are now on the market through Emergency Use Authorizations (EUAs) given out by the FDA based on a less stringent set of requirements. This is a good and bad thing, because it allows us to test in some capacity for this virus, but some tests might not be as good as we would like. Notably, there are currently no FDA approved or cleared tests for COVID-19; all tests, both molecular and antibody tests, are approved with EUAs.

One of my favorite professors recently quoted Donald Rumsfeld to me: “You go to war with the army you have, not the army you might want or wish to have at a later time.” I think this is the best way to describe our currently available antibody tests. There are four different methods used to detect antibodies, and some methods can take days, and others may take hours to complete. The hope for antibody tests is to tell us whether a patient was previously infected with COVID-19, which in theory, would imply the individual could have COVID-19 immunity. Per the Center for Health Security through Johns Hopkins Bloomberg School of Public Health, there are six tests that have been approved for diagnostic use in the United States, and some of those tests released two important metrics used to tell us how well a test may work: sensitivity and specificity. A highly sensitive test means the test should catch all true positive cases. This means the test is correctly identifying every person who does have the disease. High specificity means the test should rule out all true negative cases. This means the test is correctly identifying every person who does not have the disease. We want a diagnostic test to be highly sensitive because we don’t want to send someone home from a testing center who is a true positive for COVID-19. We want an antibody test to be highly specific, because we don’t want to tell someone they are immune to the virus, when in fact, they have never been infected – a false negative. All these numbers are based upon how many people have been infected with the virus at a specific point in time, known as prevalence. It’s notable that as the prevalence in a population changes, the sensitivity and specificity of a test will change too. Lastly, there are other viruses that belong to the same family of viruses as COVID-19, and any test needs to be able to accurately differentiate amongst these different, yet similar viruses.

We need antibody tests to have a specificity of as close to 100% as possible for their result to be reliable. The tests available now have specificities from 95.8 to 100%, depending on the test and whether the company that created them published this information. We don’t know the true prevalence of COVID-19 in our individual communities or throughout the US since many people don’t show symptoms of this. I don’t want to get too technical here, but the more people who have had the virus, the better the result of antibody testing is likely to be. As time progresses, this may make antibody tests even more useful, but that also means further viral spread will occur too.

We need good tests; otherwise, the results are widely unhelpful. There are also concerns as to how many antibodies a person may need to build immunity to this virus– and more research needs to be performed here for COVID-19. Finally, we don’t know if or for how long protective immunity will last since this virus is new to providers and researchers.

So, do you need the antibody test? The answer is, maybe. Which test is being offered at your office? Is the test highly specific? Is it currently approved for research purposes or diagnostic testing? Talk to your healthcare provider about your current or past symptoms, past exposure, and ask questions about the test provided at that office. Be understanding, kind, patient, and ask for help understanding why or if this test would be helpful for you.

Maggie Bridges Kearney is a first-year medical student at Mercer University School of Medicine. She graduated from the University of Georgia with a Master of Public Health with a concentration in Epidemiology and a BS from Georgia Tech in business administration. 

Resources used:

https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/coronavirus-disease-2019-covid-19-frequently-asked-questions
https://faq.coronavirus.gov/symptoms-and-testing/
https://www.centerforhealthsecurity.org/resources/COVID-19/serology/Serology-based-tests-for-COVID-19.html
https://www.essentialevidenceplus.com/content/eee/904
https://www.listennotes.com/podcasts/primary-care-update-mark-ebell-and-friends-s-wnlH7uvS2/