Flu (Influenza) Test

Overview

Is there a test for the flu?

Yes. Flu tests require a respiratory sample, such as a nasal swab, to check for the presence of the flu virus.

The flu (influenza) is a respiratory infection caused by a virus (germ). It occurs most often during the winter and easily spreads from person to person from coughing, sneezing and/or touching contaminated surfaces. Most seasonal flu outbreaks are caused by the A and/or B flu viruses.

What are the different kinds of flu (influenza) tests?

There are several different flu tests, including:

  • Rapid influenza diagnostic tests (RIDTs).
  • Rapid molecular assays.
  • Specialized laboratory tests.

Rapid influenza diagnostic tests (RIDTs)

RIDTs, also called flu antigen tests, are the most common type of flu test. They can identify the presence of influenza A and B, and they work by detecting the parts of the flu virus called antigens that trigger an immune response.

RIDTs usually involve inserting a swab into your nostril to get a sample.

RIDTs provide results within approximately 10 to 15 minutes, but they may not be as accurate as other flu tests. You could still have the flu even though your rapid test result is negative.

Rapid molecular assays for flu testing

Rapid molecular assays are flu tests that detect the genetic material of the flu virus. They produce results in 15 to 30 minutes and are more accurate than RIDTs.

These tests use a nasopharyngeal (NP) swab. The sample is then sent to a laboratory for analysis. Healthcare providers also use this test for people who are in the hospital and have flu symptoms.

Specialized laboratory flu tests

Other specialized laboratory flu tests are more accurate than RIDTs and rapid molecular assays. One of these tests is called reverse-transcription polymerase chain reaction (RT-PCR).

For these tests, a healthcare provider collects a sample and then sends the swab to a laboratory for testing. It may take one to several hours or days to get your results.

When do 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 a number of factors can contribute to your provider wanting you to get a flu test.

Symptoms of the flu include:

Your healthcare provider may order a flu test if you have risk factors for flu complications. Risk factors include:

  • Having a weakened immune system.
  • Having a chronic illness.
  • 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 that public health officials or providers can figure out whether an outbreak of respiratory illness in a community, such as a school or nursing home, has been caused by the flu.

Public health officials and providers may also use specialized flu tests to identify the type of flu virus that’s causing infections.

Test Details

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.
  • 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.
  • The upper part of your throat (nasopharynx) with a swab through your nose.

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 your throat or nose. A nasal aspirate or wash may feel uncomfortable, but the discomfort is temporary.

Results and Follow-Up

What type of results do you get for a flu test?

The results for a flu test that’s tested in a laboratory will be either positive (viral RNA detected) or negative (viral RNA not detected). Rarely, the result may be inconclusive or have an indeterminate interpretation.

What do the results of a flu test 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. This could mean 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 are the most accurate kind of flu test. For these tests, your healthcare provider swabs your nasal cavity or 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 that there are few false-negative results, meaning fewer cases of illness are missed. Since a rapid flu test has moderate sensitivity, it’s more likely that it’ll have a false-negative result and miss positive cases. High specificity means that false-positive results are rare.

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, are there any treatment options or medications you recommend?

Frequently Asked Questions

Is there a test than 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 are sick with the flu, COVID-19 or another respiratory infection.

A note from Cleveland Clinic

A flu test is a simple test your healthcare provider can perform on you or your child. While most people don’t need a flu test and recover from the flu within a week or two, certain factors can contribute to your provider wanting you to get a flu test. If you have any questions or concerns, feel free to reach out to your provider. They’re available to help.

Last reviewed by a Cleveland Clinic medical professional on 04/13/2022.

References

  • Centers for Disease Control and Prevention. Diagnosing Flu. (https://www.cdc.gov/flu/symptoms/testing.htm) Accessed 4/14/2022.
  • Centers for Disease Control and Prevention. Rapid Influenza Diagnostic Tests. (https://www.cdc.gov/flu/professionals/diagnosis/clinician_guidance_ridt.htm) Accessed 4/14/2022.
  • MedlinePlus. Flu (Influenza) Test. (https://medlineplus.gov/lab-tests/flu-influenza-test/) Accessed 4/14/2022.

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