Flu (Influenza) Test

Is there a test for the flu?

Yes. Flu tests use a respiratory sample to check for the presence of the flu virus. A healthcare provider will insert a long cotton swab deep into your nostril (nasopharyngeal) or around your nasal walls. A flu test is most often done at your healthcare provider’s office, in a hospital or urgent care clinic, or at certain pharmacies.

The flu (influenza) is a respiratory infection caused by a virus. It occurs most often during the winter months but can also happen in fall or early spring. It spreads from person to person from coughing, sneezing and/or touching surfaces that have the virus on them. Most seasonal flu outbreaks are caused by the A and/or B flu viruses. You can decrease the chances you’ll get seriously ill from the flu by getting vaccinated.

What are the different types of flu tests?

There are different flu tests, including:

• Rapid antigen
• Molecular assays

Rapid antigen detection

These tests work by detecting a certain flu virus protein (or antigen) in respiratory fluid from your nose. You can get the results of a rapid antigen test within 10 to 15 minutes. Antigen tests aren’t as accurate as molecular flu tests.

Other names for this test are rapid influenza diagnostic tests (RIDTs) or influenza antigen tests.

At-home antigen flu tests are available. If you choose to do this, you must follow the instructions carefully. Check with your healthcare provider to see if an at-home test is right for you.

Molecular assays

Molecular flu tests detect the genetic material of the flu virus in a respiratory sample. These tests are more accurate than rapid antigen tests. They can detect smaller amounts of the flu virus. A PCR test (polymerase chain reaction test) is a common type of molecular test.

Molecular tests can be rapid or sent to a lab. A rapid molecular flu test may give results in 15 to 30 minutes. It can take several days to get molecular flu test results that are sent to a laboratory.

When would I need a flu test?

If you have flu-like symptoms or are concerned about possibly having the flu, talk to your healthcare provider. Most people don’t need a flu test and recover from the flu within a week or two. But several factors can contribute to you needing a flu test.

Your provider may want you to take a flu test if you’re at risk of flu complications. The following factors may put you at a higher risk:

• Having a weakened immune system
• Having a chronic illness like diabetes
• Being pregnant
• Being over the age of 65 or under the age of 5
• Being in the hospital for treatment for another condition

You may also need to take a flu test so public health officials or providers can figure out if the flu is causing a respiratory illness outbreak in your community (such as a school or nursing home).

How is a flu test performed?

All flu tests require a respiratory sample. This can include samples from:

• Your nasal cavity (nostrils) with a swab around your nasal walls
• The upper part of your throat (nasopharynx) with a swab through your nose
• Your nasal cavity through a wash or aspirate, meaning your healthcare provider injects a saline solution into your nose and removes the sample with gentle suction (this collection method is sometimes used on very young children)

There isn’t any special preparation for a flu test. You can go about your day as you normally would after a flu test. The test typically takes less than five minutes.

What should I expect during a flu test?

During the sample collection, you may feel a gagging sensation or a tickle when you or your provider swabs you. A nasal aspirate or wash may feel uncomfortable, but the discomfort is temporary.

What are the risks of a flu test?

Flu tests are safe and don’t usually cause any side effects. But there are some risks. These include:

• Discomfort. Getting the fluid sample from your nose or throat can be uncomfortable and cause you to gag.
• False results. You may get a false result if the test is performed incorrectly, or your provider doesn’t get a good sample.

What do the results of a flu test mean?

Here are the possible results of a flu test and what they mean:

• Positive result. A positive result means that the test detected influenza viral antigen or RNA.
• Negative result. A negative result means that the test didn’t detect any influenza viral antigen or RNA.
• Invalid result. If your test reveals an invalid result, it means there was an error in the testing. There could have been an issue with the sample collection or the test itself. You’ll need to take another test.

What is the most accurate flu test?

Laboratory tests on nasopharynx swabs are the most accurate kind of flu test. For these tests, your healthcare provider swabs the back of your throat through your nose and sends the sample to a lab for analysis.

How accurate is a rapid flu test?

A rapid antigen flu test (rapid influenza diagnostic test, or RIDT) is the least accurate type of flu test. They have moderate sensitivity (50% to 70%) and high specificity.

Sensitivity refers to a test’s ability to determine that you have a disease or illness — you’re positive for the illness. The specificity of a test is its ability to determine that you don’t have a disease or illness — you’re negative for the illness.

A highly sensitive test means there are few false-negative results, so it misses fewer cases of illness. Since a rapid flu test has moderate sensitivity, it’s more likely to have a false-negative result and miss positive cases. High specificity means that false-positive results are rare.

Molecular tests, like a PCR test, tend to be more accurate.

When should I call my healthcare provider about my flu test?

If you have any questions about your flu test, reach out to your provider. It may be helpful to ask the following questions:

• How do you interpret my test result?
• Do you think my test result is accurate?
• Should I have any follow-up testing?
• Given my symptoms and result, do you recommend any treatment options or medications?

You should always talk to your healthcare provider about your test results and what they mean if you’re unsure.

Is there a test that can check for the flu and COVID-19?

Yes, there are at-home and laboratory tests that can check for influenza type A and B viruses and SARS-CoV-2, the virus that causes COVID-19, at the same time.

Some of the symptoms of the flu and COVID-19 are similar, so it can be hard to tell the difference between the two illnesses. If you have symptoms of the flu and/or COVID-19, contact your healthcare provider as soon as possible. They’ll likely recommend diagnostic testing, which can help determine if you’re sick with the flu, COVID-19 or another respiratory infection.

How long do you test positive for the flu?

You’ll typically test positive for the flu starting about 24 hours before symptoms begin and continue to test positive for several days afterward. How long you continue to test positive can also depend on the type of flu test you take.