Flu Test

Is there a test for the flu?

Yes. Flu tests use a respiratory sample to check if you have the flu virus. A healthcare provider will insert a long cotton swab deep into your nostril (nasopharyngeal swab) 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. There are at-home flu tests, too.

The flu (influenza) is a respiratory infection caused by a virus. It usually happens 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. You can decrease the chances you’ll get seriously ill from the flu by getting the flu vaccine.

If you have flu-like symptoms or are concerned about possibly having the flu, call your healthcare provider. They may want you to take a flu test if you’re at risk of flu complications. These 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 another condition

What are the different types?

There are two main types of flu tests:

• Rapid antigen detection. These tests work by detecting a certain flu virus protein (or antigen) in fluid from your nose. You can get the results of a rapid antigen test in under 30 minutes. This test is also called rapid influenza diagnostic tests (RIDTs).
• Molecular assays. Molecular flu tests detect the genetic material of the flu virus from fluid in your nose. These tests are more accurate than the rapid antigen test. A PCR test (polymerase chain reaction test) is a common type of molecular test. Molecular tests can be rapid (results in less than 30 minutes) or sent to a lab (results may take several days).

How does a flu test work?

All flu tests require a respiratory sample, most often from your nose (nasal cavity). The exact steps to getting a flu test depend on how your healthcare provider collects the sample.

Flu tests from a healthcare provider

• Nasal swab test. Your healthcare provider inserts a swab into your nostrils to swipe fluid from your nasal walls. They can also swab the deepest part of your nose (nasopharyngeal swab). This collection method is the most common way to get a sample to test for the flu virus. This test can give your provider a rapid result, or they can send the swab to a lab.
• Nasal wash or nasal aspirate. Your healthcare provider puts some saline into your nose, then removes a sample of nasal fluid using suction. They then send the sample to a lab. This method is helpful for infants or young children.

There isn’t any special preparation for a flu test. The test typically takes less than five minutes.

At-home flu tests

You swab your own nostrils during an at-home test (some tests may use saliva). Be sure to follow the instructions that came with your test. At-home tests can either be:

• Rapid antigen. You get results in about 30 minutes.
• Laboratory tests. You send your fluid sample to a lab using the materials in the packaging. Your test results can take several days.

What should I expect?

During the sample collection, you may feel a gagging sensation or a tickle during the swab. 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 rarely cause side effects. But like any test, there are a few things to be aware of:

• Discomfort. Having your nose or throat swabbed can feel uncomfortable and might make you gag or cough. This feeling is brief and goes away quickly.
• False results. It’s possible to get a false positive or negative — especially if the sample isn’t collected properly or the test is done too early or late in your illness.

What do the results 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 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 test?

A rapid antigen flu test (rapid influenza diagnostic test, or RIDT) is the least accurate type of flu test. Molecular tests, like a PCR test, tend to be more accurate.

When should I call my healthcare provider?

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?
• 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.

How long do you test positive?

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.