Antibody Testing: What You Need To Know

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After seeing many questions & much confusion regarding antibody testing and what it can indicate, the Porter County Health Department has developed the following to keep our citizens informed with accurate information.


Antibodies are proteins made by the immune system to help your body fight disease. COVID-19 antibody tests detect 2 possible antibodies, IgM and IgG. 

IgM is made by the body to fight a current infection. It can be detected in the blood or serum (a component of blood) of an infected person about 1-3 weeks after infection with COVID-19.  It is unknown how long it remains in the blood after an infection, but is at least 1-3 months. 

IgG is made by the body to remember an infection and help fight a future infection with the same bacteria or virus. It might prevent future infections. It can also be detected in the blood or serum 1-3 weeks after infection, but usually is found 1-2 weeks after IgM is detected. IgG may last years, but right now it is unknown how long it might last.

Antibody Tests For COVID19

Antibody tests can be done through a lab testing serum. They also can be done in an office-based rapid test with a drop of blood. All antibody tests for COVID-19 are new tests, developed since March 2020. None of them have gone through the rigorous testing requirements that are required for other lab tests. False positive tests (testing positive for the infection, but not having it) and false negative (testing negative for the infection but being infected) results can occur with any antibody test. 

Interpreting Your Test Result

Antibody tests for COVID-19 have limited clinical use. Your provider cannot say if you are contagious or can spread COVID-19 to others if you have a positive antibody test. Most people who test positive for antibodies to COVID-19 can no longer spread infection because of the time it takes to develop antibodies after the infection starts.

Your provider cannot say with certainty if you are immune to COVID-19 if you have a positive test result either, because there is not enough research to say that the antibodies are protective. Positive antibodies may also come from a past infection with a different coronavirus. If you have a positive IgG test, it might indicate that you were infected in the past with COVID-19. If you have negative antibodies you might not have been exposed to the virus yet.

Test results from antibody tests are not included in Porter County’s testing data.

The Bottom Line

If you are concerned that you have been exposed to COVID-19 and might be infected, the most accurate test to get is a nasopharyngeal (back of nose) or nasal (in nose) DNA PCR test. These tests do not give immediate results, and you will need to isolate yourself as much as possible until the test results come back, but a positive test result is very accurate to tell if you are contagious. You can obtain a nasopharyngeal test free of charge at an Indiana State Department Of Health Testing Site. To schedule an appointment at the Valparaiso ISDH testing site, VISIT HERE.

There are times an antibody test may be of interest, but the result cannot tell you if you are contagious and are not currently helpful to guide return to work determinations.