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How Does A Flu Test Work? It's Actually Pretty Simple

After hearing about the intensity of the flu is this year, even the slightest symptoms may have you feeling anxious. If you feel like you’re coming down with something or see your kids looking a little under the weather, you should probably head to the doctor’s office to get tested for the flu. If you haven't had a flu test before, you may not know what to expect. Going in for any kind of testing requires a little bit of mental preparation, especially when you have kids. So how does a flu test work?

There are actually a few different types of flu tests out there. Some are more convenient while others are more accurate, so how they work will depend on which test your doctor will use. Romper reached out to clinical pharmacist Bineesh Moyeed Pharm.D, who says that the most commonly used flu test is the Rapid Influenza Diagnostic Test (RIDT). She says that most doctors use this test because it provides quick results and is easy to administer. “The doctor will swipe your throat or nose,” explains Moyeed, “and then run a quick test to detect the influenza virus.”

If you or your kids have ever been tested for strep throat, you may be familiar with the long cotton swab used to swipe your throat. According to the ABC13 Eyewitness News, a similar swab is used in a flu test to swipe for secretions inside your nostrils or throat. After getting your respiratory secretions onto the swab, the article explained, your doctor will put the swab in a liquid for about one minute and then place a testing strip into that water. In around 10 to 15 minutes, the test strip will indicate whether or not a flu virus is present.

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Rapid tests are pretty common, but they aren’t always 100 percent accurate. According to the Centers for Disease Control and Prevention (CDC), RIDTs detect antigens — the parts of the virus that stimulate an immune response — but because these tests have limited sensitivity, sometimes they produce false negatives. Rapid influenza tests have a sensitivity range of 50 to 70 percent, noted the CDC, which means they can produce false negatives about half of the time.

There are factors that can determine the accuracy of a rapid influenza test, too. If the swab is taken too early, or the swab sample is insufficient, a rapid influenza test might show a false positive, noted NY Daily News. The article explained that to get a good sample, doctors would have to swab pretty high up into the nose, which is hard to do with a squirmy child (or adult), and if it’s within 48 hours of the onset of symptoms, the test might not be able to pick up the virus.

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The CDC noted that there are different types of flu tests, but all of them require a swab of your respiratory secretions. Rapid molecular assays are more accurate than RIDTs, the website explained, because they detect the virus’ genetic material, taking about 15 to 20 minutes to produce results. The CDC further noted that there are more accurate tests than these, but they need to be processed in a specialized laboratory (usually found in public health labs or hospitals) and can take several hours to provide results.

Moyeed explains that even if your rapid flu test comes back negative, your doctor still may treat you for the flu. “Your diagnosis and treatment will factor in your test results, what symptoms you have, your age, and any underlying health issues.” If your doctor determines you have the influenza virus, they may prescribe you an antiviral, like Tamiflu, which Moyeed says is most effective in the first 48 hours of symptoms.

So, if you are going in for a flu test, you can expect your doctor to stick a long cotton swab up your nose or inside your throat and jiggle it around for a few seconds. In comparison to the horrible symptoms this flu is causing, the flu test should be a breeze.

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