What's the Difference Between a PCR & a Rapid Test?

According to HealthLine Health News, written by Meagan Drillanger January 7, 2022 and fact checked by Jennifer Chesak.

"Rapid antigen tends to be the test for over-the-counter or at-home COVID-19 tests. You can buy them in most pharmacies. These tests come in handy when there are more virus particles in the system — when people are likely to pass the virus to another.

PCR tests, which are still typically administered by medical professionals, are much more accurate because they are more sensitive than antigen tests. PCR tests can determine whether the body has a much smaller amount of the virus and can also determine whether you’ve contracted the virus much sooner than an antigen test.

Both tests are helpful in particular situations, but they also have their drawbacks. If we are looking for a bottom line “most accurate,” then that would be the PCR test. “The PCR COVID test is the gold standard. It is excellent in diagnosing COVID when you are developing symptoms,” said Schaffner.

“However,” he added, “because it can detect viral fragments, or pieces of the virus rather than the whole virus, it can remain positive for weeks, long after the person has recovered and no longer is contagious. Thus, it is not ideal for determining the end of isolation or quarantine.”

Simply put, you can fully recover from COVID-19 and still test positive for the virus, far from helpful when you want to return to work, travel, or generally assume daily life. Similarly, the antigen test has specific drawbacks as well. They are decidedly less accurate than PCR tests when a person has a lower amount of the virus in their system. The virus is still present but may still be too low to detect. A person can have small amounts of the virus and test negative with an antigen test, which is why they are not the most reliable in determining whether a person has COVID-19.

“The rapid test has the obvious advantage of having results available within 15 minutes, but it is not as sensitive as the PCR. That is, it can register as negative when the person still is shedding small amounts of virus,” said Schaffner. “This is particularly true within the first couple of days after exposure when there still is not enough virus in the nose to turn the test positive. Nonetheless, the rapid test can be useful when gathering with vaccinated family and friends to provide an additional measure of comfort and reassurance.” Simply put, a positive test, whether PCR or antigen, should be trusted as a positive test. A negative PCR test should be trusted as negative. A negative antigen test may need to be confirmed with a PCR test."

--