We’ve all heard a lot about the COVID-19 tests in the news. But have you wondered how these tests are conducted and what exactly they are testing for? I know I was curious. After looking into it, I found that there are 2 major types of tests being used: polymerase chain reaction (PCR) and antibody testing. Let’s talk about some of the differences between the two.
As of now, the majority of tests being conducted are done by PCR. PCR allows for the detection of the RNA genome of the virus. Because this directly tests for the presence of the antigen, it indicates a current infection. The viral RNA will be present before symptoms even occur, allowing for very early detection. This is a benefit over antibody testing, as you don’t have to wait for the body to mount an immune response. However, PCR is labor intensive and there is a chance of receiving a false negative.
Alternatively, an antibody test can be done by taking blood. The downside to antibody testing is that it takes some time for the body to make these antibodies after encountering the virus. When initially exposed, after a few days the body will begin to produce IgM antibodies; a week or so after that the body begins to make IgG antibodies instead. If a person were to test positive for only IgM, it means they were very recently infected and IgG has not yet been produced. IgM has a relatively short half life, so if a person tests positive for IgM AND IgG it means they recently started making IgG and were infected not too long ago. If a person tests positive for only IgG it means they were infected in the past and have probably recovered. However, we don’t currently know if a past infection indicates this person will be immune to reinfection in the future or how long that immunity might last.
Clearly, both of these tests have their pros and cons. However, both are beneficial in letting people know that they need to self isolate to prevent further spread of the disease. Anyone testing positive with PCR, should self isolate even if they are asymptomatic as they can still spread the disease before symptoms begin to show. Detectable levels of IgM antibodies against COVID-19 also indicate active or recent infection with the potential to be contagious. With testing becoming more and more accessible in the United States, hopefully the spread of the disease will slow as more people are able to know if they have contracted it.
Microbiology by Madeline 