Coronavirus testing: Some rapid tests more accurate than others, initial research shows

Coronavirus

TAMPA, Fla. (WFLA) – New rapid tests promise you will know if you’re infected with the coronavirus within minutes.

Public health experts say rapid tests are key in this fight. But 8 On Your Side has learned not all rapid tests are created equal. Some produce much more accurate results than others.

“In general, antigen tests are not as sensitive,” said Dr. Bobbi S. Pritt.

Dr. Pritt is a Professor of Clinical Microbiology and a physician at Mayo Clinic with over 15 years of experience in the field.

8 On Your Side asked about the accuracy of the new tests coming that detect antigens.

“What we’re seeing with some of these rapid antigen tests is that they will miss up to four out of ten positive patients when they test,” said Dr. Pritt. “So, four patients will get a negative result when they are indeed actually positive.”

It’s important to stress that regardless of the test: a positive is a positive.

As Dr. Pritt explains, the concern is solely about false negatives.

Rapid antigen tests are less sensitive, meaning they’re less capable of detecting the virus in a patient’s specimen.

“Given that high – what I would call a false negative result – means the negative cannot be used to tell a person they’re not infected,” said Dr. Pritt.

8 On Your Side also spoke with Dr. John Greene, the Chief of Infectious Diseases at Moffitt, about the accuracy of the rapid antigen COVID-19 tests.

Dr. Greene, a hospital epidemiologist, has studied infections for more than thirty years.

“Those tests are fine if they’re positive, you can stop there and treat accordingly,” said Dr. Greene. “But if they’re negative, then it doesn’t give you a guarantee that you really don’t have the virus.”

Here’s the good news: The test most commonly used to detect for the coronavirus is also the most accurate.

Instead of detecting antigens, Reverse Transcription Polymerase Chain Reaction tests, or RT-PCR tests, detect and amplify viral RNA.

“The best test that we have right now is a test that detects the genetic material of the virus that’s called Reverse Transcription PCR,” said Dr. Pritt. “That is a highly sensitive, highly specific test so if the virus is present, it has a very high likelihood of detecting it.”

PCR tests can produce results in several hours or several minutes.

Currently, they are considered the gold standard.

Despite that, new data suggests even these tests can give you the wrong result about 20 percent of the time.

The problem may not be the test though. Instead, there could be a lack of the virus for detection.

“What we’re starting to learn is that early on in the disease, there may not be a lot of virus present,” said Dr. Pritt.

Bottom line: If you have COVID-19 symptoms, act accordingly, even if you test negative.

“If you come to a facility to be tested for the COVID-19 virus, they will typically run the PRC test which is fairly accurate,” said Dr. Greene.

Dr. Greene says there have been dramatic improvements in testing in the past month. There are more tests and the results are quicker.

8 On Your Side will continue to investigate every aspect of the coronavirus pandemic.

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