At the most basic level, there are two categories of COVID-19 tests; a diagnostic test and an antibody test. A diagnostic test can diagnose a current infection, whereas an antibody test can tell you whether your immune system has been exposed to COVID-19 (either via infection or vaccine) in the past. An antibody test cannot be used to diagnose a current infection.
Diagnostic tests include PCR (polymerase chain reaction) and antigen tests.
PCR is considered the “gold standard” for diagnosing infection with COVID-19. It is a molecular test that looks for COVID-19’s genetic material (RNA). PCR is very sensitive, meaning that almost everyone who actually has a COVID-19 infection will have a positive test. PCR tests are analyzed in a lab and are most often performed in a health care setting, such as a clinic, doctors’ office, pharmacy, or designated testing center. If performed at home, the sample kit will need to be mailed to a lab for analysis. The samples are most commonly collected via a nasopharyngeal swab (the swab is inserted into the nostril and up toward the back of the nose) or a salivary sample. Result turnaround can vary from ~ 1-7 days. Due to the labor of the processing, they are fairly expensive, around $150 (without insurance coverage). During COVID-19 peaks, PCR results have often been quite delayed when testing capacity has not been able to meet high demand.
Antigen tests have the advantage of speed, with results available in ~ 15 minutes. Instead of genetic material, antigen tests search for protein pieces from the COVID-19 virus. They can be purchased over the counter, are performed at home via a nasal swab, and are less expensive than PCR tests, with prices running around $20-24 per kit (two tests per kit). Antigen tests are similar in design and appearance to a home pregnancy test, with a colored line designating ‘positive’ or ‘negative’ showing in the box at the top once the sample is finished processing. Antigen tests are less sensitive than PCR tests and may be negative early on in an infection.
If you are experiencing symptoms of COVID-19 and have a negative antigen test, it is recommended to obtain a PCR test and continue to isolate until the result of the PCR test is known (if results are delayed, then continue to isolate for 5 days at minimum, with symptoms resolving and 24 hours free of fever prior to ending isolation; continue wearing a well-fitting mask for an additional five more days after the isolation period has ended).
Because PCR tests are so sensitive, they can remain positive for up to twelve weeks after a person has recovered from COVID-19 and is no longer contagious. If you have been diagnosed with COVID-19 and subsequently recovered, an antigen test is the best test to determine if you are still shedding enough virus to transmit COVID-19 to other people.
