Why you can get a negative result even when you have the flu
Rapid flu test accuracy can range anywhere from 50% to 90%, depending on the test used, individual patient factors, and how many cases of flu are in the community. Because of this, it is possible to get a negative result even though you are infected. Rapid Pregnancy
Known as a false negative, this can happen for several reasons, including when you picked up the virus and the type of flu you have.
Of course, you should also always consider the possibility that your flu-like symptoms aren't actually due to the flu and that you're testing negative because you have something else, like COVID-19.
This article goes over what it means if you get a negative rapid flu test and what to do if you think the result may be wrong.
Rapid influenza diagnostic tests look for influenza A and B viruses in fluid (secretions) from your respiratory tract.
A benefit of the tests is that the results are ready in as little as 15 minutes; other flu tests take time because they must be sent to a lab. While they're faster, rapid tests are not as accurate.
Factors that can affect the outcome of a rapid flu test include:
Rapid flu tests are a tool for providers, but results are not the only thing that matters in making a flu diagnosis. Your provider will consider all of these factors when reviewing your results to decide whether you could have the flu and need treatment.
You have the flu, but the test did not detect it
More common when community flu rates are high
The test detected the flu, but you do not really have it
More common when community flu rates are low
If your rapid test comes back negative and it's accurate, you do not have influenza. There are several different viruses that can cause flu-like illness and produce symptoms that are more severe than a common cold.
These viruses can leave you feeling very sick for a few days or even a week, and may pose a threat to people at higher risk.
If your flu test is negative but you have classic flu symptoms, your healthcare provider may test you for other respiratory viruses. However, if flu activity is high where you live, your provider may still diagnose you with the flu and and prescribe an antiviral drug, such as Tamiflu (oseltamivir), Relenza (zanamivir), Rapivab (peramivir), and Xofluza (baloxavir marboxil).
For most people, taking antivirals without a confirmed case of the flu is not as big of a risk as not treating influenza.
When they're started within the first 48 hours of getting flu symptoms, antivirals have been shown to lessen the severity of symptoms, shorten the duration of illness by about one day, and reduce the risk of flu complications.
If your symptoms do not improve with antiviral treatment, you probably did not have the flu after all. In that case, you might need different treatment. However, many over-the-counter (OTC) medications for symptom relief work for many different flu-like illnesses.
If you are sick with a respiratory virus, the Centers for Disease Control and Prevention (CDC) recommends that you:
Some providers won't do rapid flu tests because of the limited accuracy. Instead, they'll treat you based on your symptoms. However, additional flu tests can be helpful in some situations, especially if your provider thinks your flu test was a false negative.
For example, retesting is helpful for pregnant people and people who are immunocompromised or live with someone who is. In these cases, confirming a flu diagnosis helps providers make the right treatment decisions.
More accurate flu tests can be done by special labs, but they are rarely used to make a flu diagnosis in the general population aside from confirming the cause of a new respiratory illness outbreak.
When these tests are done, the results usually get sent to the Centers for Disease Control and Protection (CDC) to keep tabs on circulating flu strains and the rate of flu activity throughout the country.
If you have flu symptoms but a rapid flu test is negative, you may truly have another illness (like COVID-19 or RSV) and not the flu. However, these tests are not always accurate and there are several factors that affect the results. You may get a false negative result, which means you do have the flu but the test didn't pick it up.
Regardless of your test results, if you have symptoms of a respiratory virus, it's important to take certain precautions to avoid spreading it to others. If your provider thinks you have the flu based on your symptoms and the level of flu activity in your community, they will probably treat you without a flu test or even with a negative test.
Centers for Disease Control and Protection. Rapid influenza diagnostic tests.
Centers for Disease Control and Prevention. Influenza specimen collection.
Centers for Disease Control and Prevention. Influenza signs and symptoms and the role of laboratory diagnostics.
Centers for Disease Control and Prevention. Respiratory virus guidance.
Centers for Disease Control and Prevention. Respiratory virus guidance update FAQs.
Centers for Disease Control and Prevention. Testing and respiratory viruses.
Centers for Disease Control and Prevention. What you should know about flu antiviral drugs.
U.S. Centers for Disease Control and Prevention. Diagnosing the flu.
Centers for Disease Control and Prevention. Overview of influenza testing methods.
Epperson S, Davis CT, Brammer L, et al. Update: Influenza Activity - United States and Worldwide, and Composition of the Southern Hemisphere Influenza Vaccine. MMWR Morb Mortal Wkly Rep. 2019;68(40):880-884. doi:10.15585/mmwr.mm6840a3.
By Kristina Herndon, RN Kristina Herndon, BSN, RN, CPN, has been working in healthcare since 2002. She specializes in pediatrics and disease and infection prevention.
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