Why Your Rapid Flu Test Was Negative

False negatives and other possibilities

Rapid flu tests are useful to practitioners as they can yield results in about 15 minutes while patients are still in the office. However, false-negative results are common with these tests, meaning that you could get a negative result and still have the flu. It's also possible that your negative result is actually accurate and that the flu-like symptoms you are experiencing are due to something other than the influenza virus entirely.

rapid flu test results
Illustration by Brianna Gilmartin, Verywell

Unreliable Accuracy

Rapid influenza diagnostic tests identify the presence of influenza A and B in respiratory tract secretions. The results are ready in as little as 15 minutes, but the rapid tests aren’t as accurate as other tests that need to be sent to a lab. Accuracy of rapid flu tests can range anywhere from 50% to 90%, depending on the test, the individual, and the prevalence of the flu in the community.

Factors that can affect the outcome of the rapid flu test include:

  • How long you've been sick: Tests are most accurate when specimens are collected within three to four days of the onset of symptoms, when influenza viral shedding is highest.
  • How the sample was collected: Each test has its own specifications for specimen collection—nasopharyngeal, nasal, throat swab, or aspirate—which must be followed for accuracy.
  • The type of influenza: Rapid flu tests are better able to detect influenza A than influenza B.
  • Current flu activity: False negatives are more likely when flu activity is high, but can occur at any time. Similarly, false positives are more common when flu activity is low.

When interpreting the results of a rapid flu test, your doctor will consider all of this in the context of your symptoms and current flu activity in the community. These tests are available as a tool, but results are not the only deciding factor in making a diagnosis.

False Negative

  • You have the flu, but the test did not detect it

False Positive

  • The test detected the flu, although you do not have it

You Don't Actually Have Influenza

If your rapid test comes back negative, it is possible that you do not have influenza. Flu-like illnesses can be caused by other viruses that cause more severe symptoms than a cold. Viruses such as adenovirus, coronavirus, parainfluenza, and respiratory syncytial virus (RSV) can cause all of the miserable flu symptoms, but do not respond to antiviral medications that are effective against influenza.

While these viruses can certainly leave you feeling awful for a few days, they are less likely than influenza to lead to serious complications, secondary infections, or death.

Next Steps

If you are diagnosed with a flu-like illness instead of influenza, your treatment may differ slightly than that recommended for the flu, though it may include many of the same over-the-counter medications for symptom relief.

If your test is negative, but you have classic flu symptoms and flu activity is high in your area, your doctor may still diagnose you with influenza and prescribe antiviral drugs, such as Tamiflu (oseltamivir), Relenza (zanamivir), Rapivab (peramivir), and Xofluza (baloxavir marboxil).

The benefits of taking antivirals without a confirmed case of influenza outweigh the risk of not treating influenza for most people. Taken within the first 48 hours of becoming sick with flu symptoms, antivirals are shown to lessen the severity of symptoms, shorten the duration of illness by about one day, and reduce the risk of complications.

If your test is negative and symptoms do not improve with antiviral treatment, you likely did not have the flu.

Re-Testing

Because rapid flu tests are not always accurate, some doctors forgo testing and will treat based on symptoms. However, additional flu testing can be helpful in certain situations, especially when a false negative is suspected.

This may be particularly useful for people with suspected flu who are also pregnant, immunocompromised, or live with someone who is, as confirming an influenza diagnosis can help doctors make proper treatment decisions.

These more accurate flu 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 U.S. Centers for Disease Control and Protection (CDC) to keep tabs on circulating influenza strains and the rate of flu activity throughout the country.

During a new outbreak of respiratory illness, testing for flu can help determine if the flu virus is the cause.

A Word From Verywell

Whatever the reason for your negative flu test, make sure you understand your diagnosis and treatment options. Your healthcare provider can recommend prescription and over-the-counter medications that can help you feel better faster.

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Article Sources
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  1. Centers for Disease Control and Protection. Rapid Influenza Diagnostic Tests. Updated October 25, 2016.

  2. Centers for Disease Control and Prevention. Influenza signs and symptoms and the role of laboratory diagnostics. Updated October 26, 2016.

  3. U.S. Centers for Disease Control and Prevention. Diagnosing the flu. Updated February 23, 2018.

  4. Centers for Disease Control and Prevention. What you should know about flu antiviral drugs. Updated April 22, 2019.

  5. Epperson S, Davis CT, Brammer L, et al. Update: Influenza Activity - United States and Worldwide, May 19-September 28, 2019, and Composition of the 2020 Southern Hemisphere Influenza Vaccine. MMWR Morb Mortal Wkly Rep. 2019;68(40):880-884. doi:10.15585/mmwr.mm6840a3.