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Doctors caution: Accuracy of rapid COVID tests can be much lower than PCR

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Updated  January 25, 2022 8:59pm EST
Coronavirus in Florida
FOX 13 News

Doctor: If you have symptoms but can't get tested, assume you have omicron variant of COVID

Kellie Cowan reports

TAMPA, Fla. - When it comes to COVID-19 tests, there are two basic types: PCR and rapid. However, when it comes to accuracy, there's only one gold standard, as many are finding with the rise in cases due to the omicron variant.

"If you get a good sample, a PCR test is accurate at about 100%," explained Dr. Thomas Unnasch, global health and infectious disease researcher at USF Health. "But the trouble is they require a lab to process and could take days for a result." 

RELATED: Free government COVID test kits now available: Everything you need to know

They can also be difficult to find. A search on Wednesday for PCR test appointments at CVS locations in Tampa showed nothing available until Saturday. Combine that with the extra days it could take for results, Dr. Unnasch says it’s not worth the wait. 

"No. I would rely on the rapid tests. Even if you can’t get the rapid test, if you’re symptomatic with any sort of cold symptoms, I would just assume at this point that you’ve got the omicron variant and just stay home for five days then mask for five more," explains Unnasch. 

That’s the case, he says, for any type of rapid or antigen test, regardless of whether it’s performed by a health professional or with an at-home rapid testing kit. 

Doctors explain how and when to use free at-home COVID tests

Scientists said the at-home tests are appealing because the results come back fast, but following the instructions is critical for accuracy. Two doctors told us how and when it's best to use the tests, in order to get accurate results.

MORE: How to ensure accurate results from at-home COVID tests being sent by federal government

According to researchers, rapid tests are highly accurate when it comes to positive results, but often deliver false negatives.

"A single rapid test isn’t really useful unless you test positive. If you test positive, yes, indeed you are truly positive," says Unnasch. "But if it comes up negative, there’s a two-in-ten chance that was a false negative and you were actually positive."

RELATED: 400 million free N95 masks to be made available starting next week, White House says

Dr. Unnasch says if you feel sick but get a negative result on a rapid test, wait a day or two and test again. 

In asymptotic cases, he cautions, the accuracy of rapid tests drops off significantly. According to Dr. Unnasch, rapid tests will only detect COVID-19 60% of the time in individuals with no symptoms. 

"If you’re not symptomatic and you have no reason to think you were exposed getting tested is just as good as flipping a quarter so you might as well not even do it," says Unnasch. 

If you’re worried about an exposure, Unnasch says get yourself tested three days after the exposure to a confirmed case, then, if a rapid test comes back negative, test again on the fifth day from exposure. 

Both PCR and rapid tests are available at Hillsborough County testing sites. The tests are free and anyone can request to have both done at the same time. While some sites still have waits of upwards of 45 minutes, FOX 13 visited Tampa’s Al Lopez and West Tampa Community Center sites this afternoon and found no wait.