Health Watch: Antigen COVID-19 tests are prone to giving false positives

Coronavirus

LAS VEGAS (KLAS) — It has been nearly a month since the U.S Food and Drug Administration issued an alert which some Nevada health workers had already been warned about — COVID-19 antigen tests are prone to giving false positives.  

There are two standard daignostic tests. 

Molecular, or PCR tests, are very accurate, lab-based tests that can take days to process and get results. The test detects the virus’s genetic material. 

The other is antigen — a quick, on-the-spot test that’s less sensitive than PCR but good at identifying people who are at or near peak infection. 

The tests were validated for people with COVID-19 symptoms in the first week of symptoms. In this sceanrio, they’re pretty accurate. 

But it is trickier with asymptomatic screening. 

About 40 percent of infections are spread by asymptomatic people with high viral loads, so antigen tests, however imperfect, should not be dismissed. 

Dr. Kathleen Winston, Dean for College of Nursing at University of Phoenix, maintains wide-spread antigen testing is still the key to curb the spread. 

“You have to have a certain level of the virus in your blood stream for the diagnostic test to be accurate,” Dr. Winston said. “So, again where we’re looking for current infection, that’s the measure of the accuracy of that test. So, I have a high viral load. I have the nasal swab test for the virus. It will give me a more closely correct and accurate positive diagnosis.” 

Depending on the quality of the antigen test and the test takers, false negatives could be as high as 20 percent. 

The concern is false positives could be caused by the presence of other viruses, improper collection techniques, or other even swabs not stored at the proper temperature.  

But antigen testing technology continues to improve. 

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