Antigen Tests — Designed for Patients With Symptoms — Can Yield False Positives in Others

Maybe you're an essential worker, you're going to visit Grandma, or you just want the peace of mind a negative COVID-19 test can bring. A rapid antigen test might seem like a great idea when you're in a hurry and don't have time to wait a few days for results, but those tests are really designed for people with COVID-19 symptoms and in asymptomatic patients can deliver false positive results.

"We figured it was routine," said Wendy Frankel, who just needed a negative test for an upcoming elective surgery. "So, I went and two hours later, the nurse called me back and said that I had tested positive."

Frankel was shocked. She had no symptoms and had no known exposure to anyone with COVID-19.

Per Maryland's guidelines, she should have had the more reliable PCR test, which detects the virus's genetic material and gets sent to a lab. Instead, she had an antigen test, which looks for specific proteins from the virus and can be run at the test location with rapid results.

"I said to the nurse, ‘Should I get retested because I'm asymptomatic?’ And she said, 'No, don't bother to get retested for 10 days.'"

But if you're asymptomatic, Maryland "strongly recommends" that you do get retested. And in order to prove you had a false positive, you must get a confirmatory PCR test within 48-hours.

Luckily, Wendy got retested anyway and it came back negative. She still had to reschedule her hand surgery and spent days trying to get the positive test off of Maryland's records.

"Is that going to be a problem if down the road I have something that they connect to COVID as being a preexisting illness for insurance purposes?" she wondered.

With respiratory, neurological and even heart-related symptoms, COVID-19 is still sort of a medical mystery. The Affordable Care Act keeps insurance companies from discriminating against patients with preexisting conditions, but that law is currently under Supreme Court review.

"Lots of different ways you can run into trouble with COVID in the insurance world if the ACA protections were overturned," said Karen Pollitz, a senior fellow at the Kaiser Family Foundation who specializes in private insurance and consumer protections.

Pollitz said not only might future underwriters penalize people who've had COVID-19, with policy exclusions or higher payments, they could even target someone who's tested negative frequently.

Coronavirus Cases in DC, Maryland and Virginia

COVID-19 cases by population in D.C. and by county in Maryland and Virginia

Source: DC, MD and VA Health Departments
Credit: Anisa Holmes / NBC Washington

"Say you work in a grocery store and you come into contact with the public every day and you're worried about your exposure to COVID, insurance underwriters might look at that and say, 'They look risky, I'm going to turn them down,'" Pollitz said. 

That's certainly not a reason to avoid testing, but you definitely want the most accurate one available.

In Washington, D.C., there is no way to overturn a positive antigen test because the District's guidelines very clearly state, "DC Health does not recommend that antigen tests be used for screening people with no symptoms or known exposures."

D.C. can do that because it also has a robust testing program where anyone who wants a PCR test can get one easily — and for free. That is not the case everywhere.

"You cannot rely on the PCR test if you're not getting results in 48 hours," said Joe DeMattos, president and CEO of Health Facilities Association of Maryland.

HFAM advocates for the state's nursing homes, where two COVID-19 tests a week are required for all residents and staff. But with PCR tests in short supply and long waits for lab results, antigen tests have become a necessity. Most are being followed by a PCR test later each week.

"It's really important to go back and double check, because in a nursing home setting, when you have a false positive, the results can be catastrophic," DeMattos said.

DeMattos said nursing homes cannot move a patient to a new room with another COVID-19 patient until the positive rapid test result is confirmed with a PCR test. He's aware that even antigen test makers are clear about their capabilities.

"That is for people within the first five days of symptom onset is when you're going to get a reliable result from our antigen test," said Jeannine Mason, spokesperson for Quidel Corporation.

The company has shipped roughly 30 million antigen tests to U.S. communities, and Mason says Quidel is proud to be able to fill that need, even if places like Virginia refer to that as "being used off-label" in patients without symptoms.

"The FDA does allow for some leeway in a pandemic to say that providers and facilities can choose to use these antigen tests outside of the manufacturer's recommendations," said Dr. Surbhi Leekha, an infectious disease physician with the University of Maryland's School of Medicine.

"What they're really doing is filling this gap in our arsenal, so to speak," said Leekha. "Antigen test is better than nothing; the PCR test is better if you have access to it."

As for false positives, Virginia recommends retesting within 24 hours of the original test, if possible, and no more than 48 hours after the antigen test.

"It's a snapshot of that day and that person in that moment," said Mason. "And so that's why it's important that we have frequency of testing, that we have testing available to everybody."

In November, the FDA issued a warning to health care providers about the potential for false positives, reminding them to carefully follow instructions that come with the tests. The guidance put particular emphasis on the timing of when to read the test results and that providers should not open the test kit until immediately prior to use.

Mason said it's also possible some the false positives really were accurate and the virus was diminished by the time the repeat test was done. There have also been some issues with cross-contamination, how the tests were administered. She says the company encourages the reporting of false positives and investigates them.

Frankel got a third test, also negative, and had her surgery, but says she won't be getting any more rapid tests unless she has a known COVID-19 exposure or develops symptoms. She wants others to be aware of the concern.

"Something like this could happen to somebody else and it was very frustrating," Frankel said.

Reported by Jodie Fleischer, produced by Rick Yarborough, and shot and edited by Jeff Piper.