Flu (Influenza) Test - Understand the Test & Your Results

What is a Flu (Influenza) Test?

Flu is short for influenza, a respiratory infection caused by a virus . A flu test helps your health care provider find out if you have the flu. If do you have the flu, your provider may prescribe medicine to help fight the virus, if needed. The medicine is called antiviral medicine. It works best when started within two days after you first feel sick. Antiviral medicine may help lessen flu symptoms and shorten the time you're sick by about one day.

The flu is most common during certain times of the year, known as flu season. In the United States, flu season can begin as early as October and end as late as May. The virus usually spreads from person to person through coughing or sneezing. You can also get the flu by touching a surface that has the flu virus on it, and then touching your nose, eyes, or mouth.

Most people who get the flu will feel sick with muscle aches, fever , and other uncomfortable symptoms. They usually recover in a week or two. For certain people, such as children under age 5, adults age 65 and over, and people with long-lasting health conditions, the flu can cause very serious illness, and even death.

There are different types of flu tests:

Rapid influenza antigen tests, or rapid influenza diagnostic tests are the most common type of flu test. This rapid test can provide results in less than half an hour, but it is not as accurate as other types of flu tests.
Molecular flu tests are more accurate tests than rapid tests. A PCR (polymerase chain reaction) is a common type of molecular test. Some molecular tests provide rapid results. But the most accurate tests require sending a sample of fluid from your nose or mouth to a special lab for testing, so you will have to wait longer for the results. Molecular tests may be used to confirm the results of a rapid test.

Other names: rapid flu test, influenza antigen test, rapid influenza diagnostic test, RIDT, Flu PCR

What is it used for?

Why do I need a flu test?

If you have flu symptoms, your provider can help you decide whether you need a flu test.

Fever
Chills
Muscle or body aches
Fatigue
Headache
Runny or stuffy nose
Sore throat
Cough

Even if you have flu symptoms, you may not need a flu test. If the flu is widespread in your area, your provider may be able to diagnose you without a test. Your provider may be more likely to order a flu test if you have a high risk for developing a more serious illness from the flu, such as pneumonia . Your risk may be higher if you:

Have a weakened immune system
Are pregnant
Are over the age of 65
Are under the age of 5
Have or have had cancer
Have a chronic (long-lasting) health condition, such as asthma or diabetes
Are in the hospital

What happens during a flu test?

A flu test requires a sample of fluid from your nose or throat. There are two ways to collect a sample for testing:

Swab test. Your provider will use a special swab to take a sample from your nose or throat.
Nasal aspirate or wash. Your provider will insert a saline solution (salt water) into your nose and use gentle suction to remove it.

At-home tests are also available for flu testing. It's very important to follow all the instructions that come with your test kit. There are two types of at-home tests:

Rapid tests are done completely at home. To do the test, you usually swab your nose to collect the sample. Results are ready in under a half hour.
Self-collection tests provide a kit to collect a fluid sample to send to a lab for testing. The sample is usually a nasal swab or a saliva sample. These tests tend to be more accurate than the rapid tests you do at home, but it may take days to get your results.

Some home tests look for both flu and COVID-19 . If you're considering a home flu test, your provider can help you choose the best test for your situation.

Will I need to do anything to prepare for the test?

Are there any risks to the test?

What do the results mean?

A positive test result means you may have the flu. It's possible to have a false positive, which means your test says you have the flu, but you really don't. Depending on your health, your provider may prescribe medicine to help prevent the flu from becoming a more serious illness.

A negative result means you may not have the flu. A different virus or bacteria may be causing your symptoms. But the flu can't be ruled out. That's because a false negative is possible. That means your test says you don't have the flu, but you really do.

Rapid tests tend to have more false negatives than tests that are sent to a lab. False negatives may also happen if your test was done after the amount of flu virus in your body began to decrease. If you have a high risk for getting seriously sick from the flu, your provider may prescribe antiviral medicine even though your test result was negative. You may also need other tests to help make a diagnosis.

Some tests look for the flu and other viruses. If you had a test for more than one virus, the results will be listed separately for each type of virus.

If you have questions about your results, talk with your health care provider.

Learn more about laboratory tests, reference ranges, and understanding results .

Is there anything else I need to know about a flu test?

References

Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Flu & Young Children; [updated 2021 Oct 25; cited 2022 Apr 14]; [about 5 screens]. Available from: https://www.cdc.gov/flu/highrisk/children.htm
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Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Flu Burden: About Estimated Flu Burden; [updated 2022 Jan 7; cited 2022 Apr 14]; [about 4 screens]. Available from: https://www.cdc.gov/flu-burden/php/about/index.html
Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Influenza (Flu): Flu Symptoms and Complications; [updated 2021 Sep 21; cited 2022 Apr 14]; [about 3 screens]. Available from: https://www.cdc.gov/flu/symptoms/symptoms.htm
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Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Influenza (Flu): Information for Clinicians on Rapid Diagnostic Testing for Influenza;[updated 2020 Aug 31; cited 2022 Apr 14]; [about 4 screens]. Available from: https://www.cdc.gov/flu/professionals/diagnosis/rapidclin.htm
Johns Hopkins Medicine [Internet]. The Johns Hopkins University; c2022. Health Library: Influenza (Flu);[cited 2022 Apr 14]; [about 3 screens]. Available from: Hhttps://www.hopkinsmedicine.org/health/conditions-and-diseases/influenza
Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2022. Influenza (flu): Diagnosis;[cited 2022 Apr 14]; [about 4 screens]. Available from: http://www.mayoclinic.org/diseases-conditions/flu/diagnosis-treatment/drc-20351725
Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2017. Influenza (flu): Overview;[cited 2022 Apr 14]; [about 10 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/flu/symptoms-causes/syc-20351719
Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co Inc.; c2022. Influenza (Flu); [updated Sep 2021; cited 2022 Apr 14]; [about 2 screens]. Available from: https://www.merckmanuals.com/home/infections/respiratory-viruses/influenza-flu
National Institute of Allergy and Infectious Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Influenza Diagnosis; [reviewed 2017 Apr 10; cited 2022 Apr 14]; [about 3screens]. Available from: https://www.niaid.nih.gov/diseases-conditions/influenza-diagnosis
Testing.com [Internet]. Seattle (WA): OneCare Media; c2022. Influenza Tests; [modified 2021 Nov 9; cited 2022 Apr 14]; [about 11 screens]. Available from: https://www.testing.com/influenza-testing/
University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2022. Health Encyclopedia: Influenza (Flu) [cited 2022 Apr 14]; [about 8 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=P00625
University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2022. Health Encyclopedia: Rapid Influenza Antigen (Nasal or Throat Swab) [cited 2022 Apr 14]; [about 14 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=rapid_influenza_antigen