Antibody Testing and Case Counts - Darke County Health District

Posted on Jun 17, 2020

The Darke County Health Department has received several questions regarding antibody testing and how the results of these antibody tests may be incorporated into our county COVID-19 count.

Antibodies are Y shaped proteins that are made by the body after it recovers from a sickness. These antibodies are specifically made to be able to bind to things called antigens. Antigens are substances (usually proteins) that can be found on the surface of the body’s cells, but are also present on the surfaces of foreign invaders such as viruses, fungi, and bacteria. These antigens help the body identify what is good from what is bad. When antibodies bind to the antigens of a foreign invader, the antibodies are able to neutralize the foreign invader through a number of ways. First, by binding to the antigens, the antibodies can block the foreign invaders and prevent them from functioning normally. Second, antibodies can send out a signal to the rest of the body to alert it to the foreign invaders, allowing the body to send white blood cells to help fight off the foreign invaders. Finally, antibodies can force the foreign invaders to stick and clump together, making it hard for these foreign invaders to move in the body and easier for the body to fight these foreign invaders (1).

It is important to note, though, that just because you have antibodies against a foreign invader does not mean you were actively sick with that foreign invader. There are other ways of having or producing antibodies. One way to do this is through vaccinations. Vaccines contain weakened or dead forms of foreign invaders. By injecting vaccines into the body, your body can learn from these weakened or dead foreign invaders and thus produce antibodies against these invaders that will help your body fight off any infection (2). Another way that you can have antibodies is if you are a newborn baby. During the last three months of pregnancy, the mother will transfer antibodies to the unborn baby. Then, after birth, the newborn baby will have these antibodies for a few weeks or even months. So, for example, if the mother had antibodies against chicken pox, then the newborn baby will also have antibodies against chicken pox and will be protected from getting chicken pox for a few weeks. Yet, this passive immunity is only temporary. After two months, the newborn baby will no longer have these antibodies in their body and will have to either get vaccinations or become sick in order to develop their own immune system (3). Finally, if a person was to become very sick, they can receive a convalescent plasma transfusion from someone who has already recovered from that sickness. Convalescent plasma is simply the part of the blood that contains diseases fighting substances such as antibodies. Thus, someone who receives a convalescent plasma transfusion will receive antibodies from the donor. Yet, the use of antibodies from someone who has already recovered is still an experimental procedure and as such may carry unknown risks. There are known risks, though, such as potential allergic reactions, damage to the lungs, and transmission of infections like HIV. These risks are why only individuals who are very sick may receive antibody transfusions, as the benefit of the treatment is considered to be greater than the risks associated with the transfusion (4).

Now that we have an understanding of what antibodies are and how they work, let’s talk about antibody testing and how these tests are incorporated into our county COVID-19 count. In COVID-19 antibody testing, the presence of antibodies against COVID-19 is tested. These antibodies may be reported as just IgG, or sometimes as IgG and IgM. IgM is the first type of antibody that is produced during an infection, while IgG are the antibodies that are produced for long lasting protection (1). If IgG or IgG and IgM are present, this indicates that someone has fully recovered from COVID-19. If only IgM is present, this could indicate a current infection or a recently recovered infection (5). So, if someone tests positive for IgG antibodies against COVID-19 then they will be put under confirmed infections, right? Not exactly. Per ODH Guidelines, a case can only be considered confirmed if the actual COVID-19 virus is detected in a patient. As such, with current ODH guidelines, NO antibody tests will ever be considered confirmed. Antibody tests can only be recorded as probable. Even then, to be considered a probable case, the individual who tested positive for the antibodies must have had exposure to someone who tested positive for COVID-19 or must have had symptoms that would meet a clinical diagnosis of COVID-19. If neither of these two criteria is met, the antibody test will not be recorded in our county COVID-19 count (6). So far, as of 6/15/20, nine antibody tests have been included in our county COVID-19 count.

For more information, visit our website at www.darkecountyhealth.org.

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