Updated: Apr 23, 2020
With results from SARS CoV-2 testing now coming back from laboratories many people are looking for a resource to help them understand their results. Antibody testing for SARS CoV-2 is the newest way to try and identify if a person has either an acute infection with the SARS CoV-2 virus and the disease it causes, COVID-19, or has had a previous exposure.
If you missed our previous article regarding how SARS CoV-2 antibody testing and how to make sure you are using a high-quality laboratory for testing, you can access that article HERE.
SARS CoV-2 antibody test results from the Chambers Clinic contain information on three types of immunoglobulins (as well as four types of viral antigens). The three types of antibodies are: IgM, IgG, and IgA. Immunoglobulins are proteins made by the immune system to fight off anything the body perceives as a threat. Each “threat,” such as SARS CoV-2, has it’s own set of antibodies.
The antibody test results report:
SARS CoV-2 IgM antibodies
SARS CoV-2 IgG antibodies
SARS CoV-2 IgA antibodies
The two most established antibodies for confirming exposure to viruses are IgM and IgG. The presence of only SARS CoV-2 IgM antibodies may indicate an acute or recent infection. IgM antibodies will generally become detectable about 5 days after developing symptoms (1). IgM antibodies will begin to decline after about two weeks.
If only SARS CoV-2 IgG antibodies are present this is indicative of a past infection. IgG antibodies will appear approximately 14 days after symptoms appear and can persist for life. The presence of only SARS CoV-19 IgG antibodies may confer immunity to the virus, ie. Can't catch it again. However, because this virus is so new, how long the immunity may last isn’t precisely known.
Some results may show that both SARS CoV-2 IgM and IgG antibodies are present. In this scenario, it is most likely that the patient was recently infected with SARS CoV-2 and is in the process of seroconversion. Seroconversion is the term used to describe the process of IgG antibodies elevating and IgM antibody levels declining. This is a normal and expected part of the immune response and doesn’t happen immediately, therefore some overlap is possible. This person would be considered to have an active infection.
The utility of IgA antibodies in diagnosing or monitoring the SARS CoV-2 virus aren’t completely known at this time. Some reports have suggested that SARS CoV-2 IgA antibodies are early markers of respiratory illnesses. Additionally, analyzing levels of all three SARS CoV-2 specific antibodies can help to minimize false positive and false negative results.
It is also possible that a person’s results would not show the presence of either IgM, IgG, or IgA antibodies. In this case, it is unlikely that the person has had exposure to the SARS CoV-2 virus.
For more information or to inquire about SARS CoV-2/COVID-19 testing please contact our offices at 480-389-3265