What is a COVID Test?

It may surprise you to learn that there is no test for COVID-19, the disease of the pandemic.  Instead, tests look for SARS-CoV-2, the virus known to cause COVID-19, or the body’s response to SARS-CoV-2.  These different tests are all commonly (but inaccurately) called “COVID Tests”, probably because it is easy to say.

Tests for SARS-CoV-2, like all laboratory tests, have two phases: pre-analytic and analytic.  The analytic phase occurs within the walls of the laboratory at the testing bench.  The pre-analytic phase includes all activities that occur up to the time that the specimen is placed on the analyzer in the laboratory, including specimen collection and transportation.

A direct test for the virus requires collection of a sample by swab.  The greatest concentration of virus is found in the back of the nose (“nasopharynx”), so that is where most swab collections are taken, but virus may also be found in other places in the body, including the middle portion of the nose and in saliva.  Collection can be uncomfortable.  There is no blood test that can directly detect the virus.  Most drive-through “testing” centers are actually drive-through collection centers since very few actually analyze samples on-site.  Most of these sites send their collections to a large central laboratory for analysis. 

A test for the body’s response to viral infection is known as an antibody test.  The antibody is present in the bloodstream, so a blood sample is all that is needed for this test.  There is a time lag between infection and detectable antibody in blood, so an antibody test is not useful to detect patients that might infect others.  Therefore, antibody tests have had limited utility during the present pandemic. 

The most accurate test for SARS-CoV-2 is the PCR test, which will be the subject of the next blog.