Asked & Answered: How reliable are COVID-19 tests?

Infectious disease doctors says reliability depends on two factors
COVID-19 testing at Savannah Civic Center
COVID-19 testing at Savannah Civic Center(WTOC)
Updated: Jul. 23, 2020 at 2:00 PM EDT
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SAVANNAH, Ga. (WTOC) - Testing is a key component to getting out of a surge in new COVID-19 cases, health care expects have said.

This week, new testing sites have opened in Richmond Hill and Savannah.

That’s prompted calls into the WTOC newsroom from viewers who have asked: How reliable are the COVID-19 tests?

The tests are largely accurate, but like with any test, there’s a chance of it being wrong, said Dr. Stephen Thacker, an infectious disease doctor at Memorial Health.

Here’s what he had to say.

A viral test is the kind most people think of - the one where a healthcare provider swabs the inside of a patient’s nose. The reliability of those tests largely depends on two things: the kind of test and the person administering it.

“There are some tests that are being used on the market that have about a sensitivity or the ability to detect the virus reliably of about 75 percent, but when it’s positive - it’s positive because you have the infection so the specificity is 100 percent,” said Dr. Stephen Thacker, an infectious disease doctor at Memorial Health.

He explained hospitals use a different test for admitted patients - one that's more reliable - about 95 percent accurate.

“And if it’s positive, it’s generally not a false positive,” Dr. Thacker said. “It’s proof that you have infection.”

So what is a false positive? It means you don't have the virus but the test shows you do.

The chances of that happening, Dr. Thacker said, are extremely low compared to the chance of a false negative.

A false negative means you have the virus, but the test says you don't.

“(The test) needs to be done correctly to get a reliable sample, so the test gives a reliable result,” he said. “So, when we have a false negative, usually the answer is how it was obtained.”

A proper sample collection is key to a reliable results. The person being tested plays a big role.

Local health guidance advises someone who has been exposed to wait until he or she has symptoms of the virus before being tested. Or if there are no symptoms, a person exposed should wait until the 10th day since exposure to be tested.

Otherwise, a test too early after exposure could produce a false negative, meaning there aren’t enough virus particles in the body for the test to detect it, according to information on the Coastal Health District’s website.

Something else to know: Recently, the demand for testing has increased in this area, and so has the wait time for those results. For some, the turnaround has taken between four to five days to get back lab results.

If you have questions about whether you should get tested, talk with a health care professional.

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