There are three different types of tests – molecular, antigen and antibody tests. The most common molecular test is the polymerase chain reaction (PCR) test. Molecular and antigen tests are both considered to be diagnostic tests.
A PCR or antigen test is used to identify an active coronavirus infection. PCR tests detect the COVID-19 virus’ genetic material. The antigen test detects proteins on the surface of the virus.
The antibody tests looks for antibodies that are made by a person’s immune system in response to a COVID-19 infection. According to the FDA, antibodies most commonly become detectable 1–3 weeks after symptom onset, at which time evidence suggests that infectiousness likely is greatly decreased and that some degree of immunity from future infection has developed. Antibody tests are commonly used to determine if the test subject has previously had a COVID-19 infection.
The table below summarizes the primary types of COVID-19 tests.
Source: Coronavirus Testing Basics, CDC, July 2020