A polymerase chain reaction or PCR test is a test that looks for the virus’ RNA in a patient’s sample. A sample is collected by inserting a swab into a person’s nostril and taking cells from the back of the nose (nasopharyngeal swab). Some lab tests allow for patients to spit into a tube to get a saliva sample. PCR tests are accurate when properly performed by a health care professional, but rapid tests can miss some cases.