Why Was My Flu Test Negative?

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Question: Why Was My Flu Test Negative?

A reader says: I have been suffering from classic flu symptoms — body aches, fever, cough, and headache — for two days. I went to see my health care provider, and he performed a flu test. The results came back negative. I don't understand. I was sure I had the flu. Now what?


It does sound like you had many common flu symptoms. In your case, most likely one of two things happened:

The test was wrong.

This is actually pretty common. The rapid flu tests that most health care providers use are a great tool, but they can be wrong. Accuracy can range anywhere from 50 - 90%, depending on the test and prevalence of the flu in the community. False negatives are more likely when flu activity is high, but can occur any time. Similarly, false positives are more common when flu activity is low. Unfortunately, it's not as simple as just buying the most accurate test: factors such as how long you've been sick, the type of specimen that was taken (typically a nasal or throat swab), and the type of influenza virus can all affect the outcome of the rapid flu test.

More accurate tests can be performed by specialized labs, but these are rarely collected in the general public just to make a diagnosis. Most often, these tests are performed, and results are then sent to the CDC so they're able to keep track of the strains of influenza that are circulating, and the level of flu activity throughout the country.

If your health care provider suspects the flu test was incorrect because you have so many of the common signs, he may still diagnose you with the flu. The rapid flu tests are available to health care providers as an additional tool but are not used as the deciding factor when making a diagnosis.

    You don't have the flu, you have a "flu-like illness".

    Although we talk a lot about the severity of the flu and how it is different from a cold, there are other viruses out there that cause very similar symptoms and can make you feel pretty miserable — but they aren't influenza. These viruses can cause all of the common flu symptoms, but they aren't technically the flu and won't be affected by the antiviral medications that are sometimes used to treat it. They also can't be prevented by getting a flu vaccine.

    While these viruses can certainly leave you feeling miserable for a few days, the good news is that they aren't as likely to lead to serious complications or secondary infections as the flu, and definitely don't cause the number of deaths that influenza does.

    If you are diagnosed with a flu-like illness instead of influenza, your treatment may differ slightly, but you can use many of the same over-the-counter medications and other treatment options since your symptoms are similar.

      Whatever the reason for your negative flu test, make sure you understand your diagnosis and what your treatment options are. Talk to your health care provider about what she thinks is causing your symptoms and what you can do to feel better, or signs to look for in case things change. You may have the flu and you may not, but something is making you sick, and you need to know what you can do to quickly get back to normal.


      Rapid Diagnostic Testing for Influenza Seasonal Influenza (Flu). 8 Dec 10. US Centers for Disease Control and Prevention. Department of Health and Human Services. 15 Mar 13.

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