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Can A Flu Test Be Wrong? Don't Put All Your Eggs In One Basket

Last week, a 6-year-old in New Jersey was reportedly turned away from the hospital with a 104-degree fever after her flu test came back negative, as The Jersey Journal reported yesterday. Shortly thereafter, she slipped into a coma and died. What happened is deeply troubling and is causing many to wonder: Can a flu test be wrong?

The short and scary answer is: Yes, a flu test can be wrong and give a false negative. Because the rapid test isn't perfectly sensitive, the Centers for Disease Control and Prevention (CDC) have instructed healthcare providers to diagnose influenza based on symptoms, not just test results.

"I think there’s a lot of misconceptions even in the medical field about flu," says Dr. Pat Salber, a former ER physician now of The Doctor Weighs In, in an interview with Romper. "We know that the tests that take 24-hours to come back are really reliable, but it’s unclear if people understand that the rapid antigen tests are not." In an emergency situation, you're more likely to receive the rapid antigen test if doctors want to verify that you have the illness. However, because it's not a very reliable test, not all doctors will bother to test at all. Importantly, flu can be diagnosed by symptoms and context alone.

Of course, any medical test can potentially return a false negative — but in the case of rapid tests for influenza, it happens a lot. In fact, up to 50 percent of patients with the flu get false negative results, reported Emergency Physicians Monthly. Because of the test's low sensitivity, Dr. Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security, tells Romper that it's "dangerous" to rely on these tests to rule out the virus. And in the case of the flu strain currently wreaking havoc across the country — the doctor-dreaded H3N2 — rapid test sensitivity may be even lower than usual. According to the CDC, false negative flu tests are particularly likely when the season is at its peak.

Because false negative flu tests occur so frequently, the CDC recommends that providers "use clinical signs and symptoms, medical history, physical examination, and information on local influenza activity in the community to decide if antiviral treatment is needed." Especially if a patient is at risk of complications, doctors shouldn't wait for a second test to come back before starting antiviral treatment.

According to Salber, the rapid flu test has a relatively low sensitivity, between 50 and 60 percent. That means that a negative result doesn't mean as much. Especially when flu is pervasive in the wider population, as it is this winter. "If it’s negative, you miss a lot of cases," she explains. However, not all providers understand the limitations of the rapid flu test. "The diagnostic accuracy of influenza swabs is often overestimated by clinicians," explained Emergency Physicians Monthly.

So far in a deadly flu season, 84 children have lost their lives, reported the CDC. (As The Washington Post observed, that number might be low.) When kids die from the flu, Salber explians, they're usually not dying from the complications, like pneumonia, that older people incur. Rather, kids are dying from a tricky immune response known as cytokine surge.

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"The deaths are astonishingly rapid," says Salber. "I think the big thing this season is to make sure that families understand, that they become advocates for their kids and themselves, are able to say, wait a minute, have you thought that maybe that test isn't sufficient?"

Especially when the result is negative, it's important for families and patients to understand that the flu test might not tell the whole story, and if you as a parent are ever in doubt of the result, be sure to seek an additional opinion.

Check out Romper's new video series, Bearing The Motherload, where disagreeing parents from different sides of an issue sit down with a mediator and talk about how to support (and not judge) each other’s parenting perspectives. New episodes air Mondays on Facebook.