What is a PCR test?
The polymerase chain reaction (PCR) and nucleic acid amplification tests (NAATs) are molecular tests. Molecular tests detect the presence of the virus’s genetic material, known as RNA. In general, these tests are considered to be the “gold standard” for diagnosis of COVID-19. They have greater sensitivity than antigen tests, meaning they can detect more people who have COVID-19 infection. It typically takes about 24 hours to get PCR test results, but results can take even longer if labs are backed up.
What is an antigen test?
Antigen tests, also referred to as rapid tests, detect the presence of one or more proteins that are part of the virus. Antigen test results can be acquired quickly because they require less complex technology. They frequently have a faster turnaround than molecular tests, and you can get results from a doctor’s office or urgent care very quickly. Home antigen tests can also be purchased at drug stores and online — several have been cleared by the Food and Drug Administration under an Emergency Use Authorization. The rapid home tests are a good tool to have on hand, especially when it’s difficult to find a PCR test and you develop symptoms.
False positive results on antigen tests are rare, but because antigen tests have lower sensitivity, a false negative result is possible. This is important because a negative antigen test does not necessarily mean you don’t have the virus. If you have symptoms of COVID-19 or have reason to suspect you were exposed, such as having close contact with someone who subsequently tested positive for COVID-19, it’s recommended you confirm a negative antigen test result with a PCR test. It is also important to note that a negative test (either antigen or PCR test) immediately following an exposure to someone with COVID-19 does not prove you were not infected, because it can take several days for the virus to become detectable.
When should people get a test?
While specific recommendations vary among local and state health departments and other agencies and employers, groups prioritized for testing are people with symptoms of COVID-19 and those with known exposure to COVID-19. Other situations in which testing has been recommended include before and after traveling and attending large gatherings, prior to invasive medical procedures and surgery, and for people who work or live in a long-term care facility or another congregate residential setting.