How common are false-positive COVID tests? Experts weigh in.

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PALOS VERDES ESTATES, CA - AUGUST 24: A rapid COVID-19 test swab is processed at Palos Verdes High School in Palos Verdes Estates on Tuesday, August 24, 2021. The district is encouraging all students and staff to test before the first day of school, August 25, and there are three sites for the drive-up testing. (Photo by Brittany Murray/MediaNews Group/Long Beach Press-Telegram via Getty Images)
A rapid COVID-19 test swab is processed. (Photo by Brittany Murray/MediaNews Group/Long Beach Press-Telegram via Getty Images)

Sunny Hostin and Ana Navarro were cleared to return to The View Monday after the co-hosts made a dramatic exit from the show on Friday. Both Hostin and Navarro, who are fully vaccinated against COVID-19, were told on-air that they had tested positive for COVID-19.

Navarro later called into Anderson Cooper 360º and said that the moment felt "like an episode of 'Curb Your Enthusiasm.' It was just surreal." Navarro, who is a regular guest host on the show, explained that she is tested for COVID-19 weekly as part of her job. She said during the interview that she later took another rapid antigen test and a PCR test, which both gave her negative results.

Both hosts were in the studio on Monday. Co-host Joy Behar said that the entire cast and crew of The View were given "numerous, numerous" tests over the weekend, and all were negative.

"I am thrilled to report that Sunny and Ana's Friday results turned out to be false positives and everyone is safe, healthy and COVID-free," Behar said. "No one's got it. It was a mistake of some sort."

But Hostin and Navarro addressed the fallout of having their results shared so publicly before they even had time to process them. Hostin said that it was "really uncomfortable for my results to be released publicly before I even knew what was going on, before they were verified, before I was tested again and again." 

"My husband is a surgeon. ... He was in the operating room and had to be pulled out of the operating room because God forbid he's operating on someone and he's COVID-positive," she said. "My child's school had to be notified and she had to be pulled out; my parents had to be rushed to be tested."

Navarro said she was "flabbergasted" about her positive result, and noted that Donald Trump Jr. took a dig at her weight after the news went viral. "Baby, if you want to have a conversation about COVID and obesity, you could have had it last October when your elderly obese father had it," she said. "It is a legitimate conversation to have, and fortunately for you, you've got somebody in your family you can call and discuss it with. Because imagine having a father whose butt is the size of a studio apartment in New Jersey and you've got the gall to pick on me?"

The drama surrounding the hosts' exit naturally raises some questions about how common it is to get a false-positive result from a COVID-19 test. It's important to note that there are different COVID-19 tests available, and each has its own level of accuracy. Two of the most common tests are rapid antigen tests (which are often used for at-home tests) and polymerase chain reaction tests (PCR), which are sent to a lab and are considered the gold standard for COVID-19 testing.

The Food and Drug Administration has issued emergency use authorizations (EUAs) for several rapid tests that don't require prescriptions. The most common include the Abbott BinaxNOW Self Test, the Quidel QuickVue At-Home OTC COVID-19 Test and the Ellume COVID-19 Home Test.

Accuracy varies among each test, but Ellume says that its test has a 96 percent accuracy rate in detecting symptomatic cases of COVID-19 and 91 percent accuracy in detecting asymptomatic cases; BinaxNOW says it picks up 84.6 percent of positive COVID-19 cases and 98.5 percent of negative cases; and QuickVue's test results record 83.5 percent positives, with negative results at 99.2 percent. 

Related video: What you need to know about COVID-19 false positives

The accuracy of PCR tests varies, depending on when someone is tested. However, one study found that the false-negative rate can be as high as 20 percent when a person is tested five days after developing symptoms. It's much higher — nearly 100 percent — when they're tested before that, though. The false-positive rate for a PCR test is close to zero, though. 

The probability for false positives varies by each type of home test, but Ellume specifically says on its online FAQs that "there is a chance that this test can give a positive result that is incorrect." Ellume notes that "the percent of positive test results that are true positives (also known as Positive Predictive Value or PPV) varies with how common infection is in a population."

Here's how it works, according to Dr. Thomas Russo, professor and chief of infectious disease at the University at Buffalo in New York. As the amount of COVID-19 in a community decreases, there's a greater chance of getting a false positive "simply because no test is 100 percent," he tells Yahoo Life.

"There's a pre-test probability that if you're screening a whole bunch of asymptomatic people and there is a low community burden of disease, the majority of positives will probably be false," he says. "That's just what happens when you do the math."

"This is one of several reasons why many of us— including the Centers for Disease Control and Prevention— do not recommend testing asymptomatic vaccinated individuals," infectious disease expert Dr. Amesh A. Adalja, a senior scholar at the Johns Hopkins Center for Health Security, tells Yahoo Life. False positives "can happen with any test" and, if someone tests positive for COVID-19 with a rapid test but does not have symptoms, he recommends following up with a PCR test to confirm that this is a "true positive."

Rapid COVID-19 tests are becoming more popular, and a growing number of people are keeping these in their homes just in case. So, how can you use them properly to make sure you don't end up in a similar situation as "The View" hosts?

If you or a member of your household tests positive for COVID-19 with a rapid test and you're having symptoms of the virus, Adalja says, it's very likely it's a true positive. "You're testing someone who has a high pre-test probability of being positive because they have symptoms," he explains.

If you test negative for COVID-19 but you're having symptoms of the virus, Russo recommends either getting a PCR test or using a rapid test again the next day (and being cautious about your contacts in the meantime). Worth noting: Both BinaxNOW and QuickVue recommend that you take two tests at least 24 to 36 hours apart to get the most accurate results.

If you have no symptoms and are testing before a wedding or visiting an at-risk family member, Russo recommends doing successive testing, just to be sure. "The strength of these home tests and rapid tests are when you do daily testing," Russo says. "Then, if you have no symptoms and you test negative, you're very likely good."

But, like Adalja, Russo doesn't recommend testing for COVID-19 if you're symptom-free. "In the absence of symptoms, you have to ask yourself what you’re doing this for," he says. "If you're fully vaccinated, the likelihood is very high that you’re negative."

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