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Why rapid COVID tests are not as reliable

Some countries are now requiring a more extensive PCR test for entry

ATLANTA — Some COVID-19 tests are more reliable than others, and faster is not always better. Rapid COVID tests will give results in just minutes, but medical experts say there is a risk of false-negative results.

“The problem is, if you get a negative, you may be positive and you didn’t detect,” said Dr. Jose Cordero of the University of Georgia’s College of Public Health.

For travelers, countries all over the world are requiring negative COVID tests before you can enter. A few like Bermuda, Ireland, the Turks and Caicos, and Turkey are requiring the more reliable PCR tests. That’s the test that searches for genetic material unique to COVID-19. The results can take several days.

The rapid, or antigen test, looks for proteins unique to the coronavirus. Results can come back as quickly as 15-minutes. The rapid test reacts to a swab taken from a patient then changes color indicating a positive or negative result.

Dr. Cordero said a PCR test is more involved.

“You’re getting a sample, there’s a process of extracting the RNA (genetic material),” said Dr. Cordero. “There are several processes and all of them take time.”

If there is a large amount of virus present, the rapid test will likely find it. Otherwise, it could miss signs that someone is sick.

“The rapid test is looking for the low-hanging fruit,” said Dr. Cordero.

If you’re searching for apples in a tree that’s flush with fruit you can have success with a quick search. If the apples are hidden at the top of the tree, a rapid search might conclude there are no apples to find. You need the work of the PCR test to take the time needed to locate what you’re looking for.

Dr. Cordero said rapid tests are useful in some situations like a quick assessment in a community with an outbreak.

For people with symptoms of COVID-19, if they get a rapid test that comes back negative, it’s best to be sure by undergoing a more extensive PCR test.

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