Are rapid COVID-19 tests accurate?

Doctor says yes, but less accurate than other tests
Posted at 10:47 PM, Aug 24, 2020
and last updated 2020-08-24 23:31:03-04

CUYAHOGA COUNTY, Ohio — Many people have questions about the reliability of rapid COVID-19 tests and whether they yield false negatives or false positives at times.

Three Mayfield volleyball players who tested positive for COVID-19 received rapid tests, according to a release from the school district. Rapid tests also led to confusion in the NFL over the weekend, when players in the league, including some on the Cleveland Browns, received false-positive test results.

It's not clear what type of rapid tests these athletes received. However, doctors say rapid antigen tests, which look for proteins on the outer shell of the virus, are less sensitive and less accurate than tests that take longer. Rapid antigen tests have more false negatives and occasional false positives.

"You might have some false positives," said Dr. Christine Schmotzer, chief of the division of clinical pathology at University Hospitals. "But the benefit of that is you take any chance to prevent somebody from exposing somebody else."

Schmotzer said testing for coronavirus comes in two forms: diagnostic testing, which tests whether someone has the virus right now, or antibody testing, which is whether you had the virus in the past.

One of the two types of diagnostic testing looks for genetic material or nucleic acid sometimes referred to as a PCR test or testing the RNA. The other type is antigen testing, which tests the protein on the outer shell of the virus.

Both types of testing can be done by rapid methods, Schmotzer said, but she said antigen rapid tests are becoming increasingly available.

"The nucleic acid or the genetic material tests that are not rapid are the ones that are going to be the most accurate," Schmotzer said. "So they'll detect the least amount of virus, the earliest in the illness, and have the least amount of cross-reactivity with things that are not the SARS-CoV-2 coronavirus."

Rapid nucleic acid tests will be "a little less sensitive, so you might miss some individuals who have coronavirus, so you won't have enough virus to detect it," Schmotzer said.

However, those tests are very specific and lead to fewer false positives. When you move to rapid antigen or protein tests, according to Schmotzer, that's when more false negatives and occasional false positives can come into play.

"They need a lot more virus to be present because of positive results than you do with the nucleic acid test, so you're at higher risk of missing a true positive result," Schmotzer said.

While Schmotzer said it is difficult to give percentages for accuracy with these tests, because they are so new, she said it's important to take into account how likely a person is to have the disease when they come for the test and the context in which they're tested.

If someone with clear COVID-19 symptoms (such as fever, shortness of breath and dry cough) receives a negative test result on a rapid test, "we would be very concerned that it's a false negative in that patient because their symptoms really make it sound like they have COVID-19 disease," Schmotzer said.

But if someone comes in with no symptoms, feeling well and with no exposure to COVID-19 patients, a negative test result is more likely to be a true negative.

Although antigen tests are less sensitive, Schmotzer said they have a place.

"Sometimes speed is important and sometimes it’s, you know, if you have somebody that's infectious in that moment, the rapid tests will identify people who are strongly infectious in that moment. People who have a lot of virus present," Schmotzer said.

But it's important to think about the setting and the risk of having a false positive or negative. In certain circumstances, such as in a hospital setting, she said the most sensitive PCR or genetic material tests are best in order to minimize a false negative result that could expose someone else to the virus.

"You have to take it into a context of what action you're going to take on result," Schmotzer said. "Who is at risk if the result is wrong? What are the consequences?"

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