ADPH: Rapid COVID-19 test could produce false negatives

Updated: Sep. 22, 2020 at 5:00 PM CDT
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HUNTSVILLE, Ala. (WAFF) - Alabama’s public health experts are raising concerns over rapid COVID-19 testing and the risk of false negatives.

The Alabama Department of Public Health said if you receive a negative result from a rapid antigen test, there is a 20 percent chance that negative could really be a positive.

If your coronavirus test is negative, there is a possibility it shouldn’t be.

“That does not mean they don’t have COVID,” said Doctor Karen Landers with the Alabama Department of Public Health. “It just means the test was negative because there was not enough material there to get to reach the threshold of positivity or potentially sometimes it could be the technique.”

Currently, there are two major COVID-19 tests on the market.

PCR tests check for genetic materials of the virus. It takes at least 24 hours to get results.

Antigen tests look for proteins on the outer shell of the virus, results come back in 15 minutes and tests are cheaper.

“Now both tests are very specific. If a positive, test positive, it’s a positive," Landers said

But Doctor Landers said antigen tests are less sensitive and less accurate than tests sent to a clinical laboratory.

“Any test is just a snapshot. Any test could be negative based upon different variables. You can’t hang your hat on a negative test if you have a clinically compatible situation," she added.

The antigen test is good when treating symptomatic people, false negatives are more likely when asymptomatic people receive an antigen test.

“I think rapid testing has a place in Covid-19, but you have to remember your accuracy is higher with the PCR by going to the commercial laboratory."

If you are testing people daily, the false negative rate is less important because you are doing the test over and over again. A saliva test can also be tested quickly, public health experts hope to see those tests in nursing homes and schools soon.

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