What Is Antibody Testing?
As the coronavirus (COVID-19) spread around the world, we learned that it affects different people in different ways. Once a person is infected, the symptoms can range anywhere from minimal to extremely severe or somewhere in the middle. Mild symptoms like a low-grade fever, sore throat, cough, muscle pain and shortness of breath are sometimes mistaken for other health problems like the flu and common cold. Today, the reality is not everyone who has recovered from COVID-19 is aware that they have been exposed to the virus.
As we learn more about the virus, evidence suggests that some people may have been infected by the coronavirus earlier than we previously thought. Antibody testing is one way that we can help improve our knowledge of COVID-19. Specifically, this testing may help us either identify the true number of people who have been exposed to the coronavirus or give us a better estimation of those affected which may help in the development of new strategies to fight the virus.
In early December 2020, the Centers for Disease Control and Prevention (CDC) updated their recommendations regarding COVID-19 exposure quarantine. While this doesn't apply to healthcare workers and other essential personnel, the guidance now states that quarantine can end after 10 days (rather than 14) with no testing and no symptoms. Quarantine can end after seven days with a negative test and no symptoms.
What is Antibody Testing?
Antibodies are the proteins that the body creates to fight off infections. Antibody testing or serology testing involves analyzing a person’s blood to determine the presence of these proteins which may indicate if the person being tested has been infected or exposed to the virus. This kind of testing allows doctors and epidemiologists to get a better handle on the true spread of the virus, as well as to understand the number of people who have been infected especially those individuals who may have had minimal symptoms.
Different types of antibodies exist and serve different functions within the body. Doctors may order tests for two different types of antibodies in particular, IgG and IgM. Doctors test for two different antibody types because one or both of these tests may be positive depending of the timing of the illness/exposure and the antibody test. IgM antibodies often turn positive first while IgG may take a little longer. However, IgG antibodies are likely to remain positive while IgM may turn back to being negative after a period of time.
Antibody testing is different from coronavirus testing, which screens for the presence of the virus in the body. One cannot substitute for the other, as the coronavirus test measures the presence of the virus in your body while antibody testing measures if your body has responded to coronavirus.
Infection vs. Immunity
We know that for some infections including influenza and other vaccine-preventable diseases, the presence of antibodies helps provide some protection or level of immunity from that infection/disease. However, based on the information that is currently available, scientists and doctors have not yet been able to conclude that the presence of coronavirus antibodies in the blood provides any level of immunity or protection from the coronavirus infection. In other words, testing positive for coronavirus antibodies whether IgM, IgG, or both, indicates you have been exposed in the past. However, a positive antibody test does not indicate at this time that you can’t be re-infected by the virus at some point in the future. Researchers are currently working to identify which antibodies and how many of them are needed to have an impact and prevent reinfection.
The information in this blog post is accurate at the time of publication. However, as the situation surrounding COVID-19 continues to change, it's possible that information has changed since being published. While Ochsner Health is trying to keep our blog posts as up-to-date as possible, we also encourage readers to stay informed on news and recommendations by using the CDC website.