I listen to Dr Michael Osterholm‘s weekly podcasts on the coronavirus pandemic. Last week he talked about, among other things, the different types of tests and what each is good for. I found it interesting and thought you might, too. (I cannot guarantee that I got all of it exactly right. Check out the FDA link below for more authoritative info.)
Diagnostic tests. This is the RT-PCR test, which has both high sensitivity and high specificity. This the test for folks who have COVID-19 symptoms or who have had a known exposure to the virus. It will tell them with a high degree of accuracy whether they are infected.
Screening test. This is a rapid, point-of-care test using the subject’s saliva. It should be used on people who are asymptomatic and have no known exposure. It is 10% or more less sensitive than the diagnostic test.
Surveillance test. This test is useful to know what is happening in a community, and the results are not necessarily returned to the subject. A large number of blood samples are tested for antibodies to determine the prevalence of coronavirus in a given community. This is the antibody test; it can give false positives, but testing at weekly/monthly/quarterly intervals will show community trends.
The FDA has more detailed information about the various type of tests here.