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?

Flu tests are used to help you find out whether you have the flu. Flu tests are also used to watch for flu outbreaks in the community and for identifying the type of flu virus that is causing the infection.

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?

You don't need any special preparations for a flu test.

Are there any risks to the test?

If your throat or nose is swabbed, you may feel a gagging sensation or even a tickle. A nasal aspirate or wash may feel uncomfortable. These effects are temporary.

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?

Getting a yearly flu vaccine (flu shot) is your best protection against serious illness from the flu. The Centers for Disease Control and Prevention (CDC) recommends the vaccine for most people 6 months or older. If you have questions about the flu vaccine, talk with your health care provider.