a nurse helping a man use a FeNO machine

How FeNO Testing Can Aid Asthma Diagnosis and Treatment

Have you ever heard of FeNO testing for asthma? It is a type of test that was recently endorsed by the updated Asthma Treatment Guidelines. A national panel of many different types of asthma experts has created this comprehensive guide to diagnosing, treating, and controlling asthma. It is meant to help health care providers and people with asthma work in concert to manage asthma.

The guideline is based on the best research-based treatment options.1 For the first time in over 10 years, the panel updated it to reflect changes in our knowledge about asthma and asthma treatment. The changes focused on 6 areas. One of those was the use of FeNo testing.

What is a FeNo test for asthma?

FeNO is short for fractional exhaled nitric oxide testing. It can measure how much inflammation there is in your airways.2 It does not specifically test for asthma. But in people ages 5 years and older, it is one of the things that can help a doctor make an asthma diagnosis.

When your airways are inflamed, as is the case with allergic or eosinophilic asthma, the cells involved in this inflammation produce a gas called nitric oxide.3 This gas is present in the air you breathe out. The higher the level of nitric oxide, the more inflammation there is in your airways. Measuring this nitric oxide level can give your doctor clues to your actual lung health, even when you feel as though your breathing is still okay.

The FeNO test uses a portable, handheld device with a mouthpiece that you breathe into. This device measures how much nitric oxide, in parts per billion, is in the air you exhale.3 One of the differences between the FeNO test and other lung function tests, such as spirometry, is in the way you breathe into the device.3 With spirometry, you must exhale hard and fast for it to measure accurately. FeNO testing is easier because you need only exhale slowly and steadily.

This test is not meant to be a stand-alone method for diagnosing or treating asthma, but it can be a helpful tool.

Who should have a FeNO test to help diagnose asthma?

To make a diagnosis of asthma, doctors use a combination of methods, including:2

  • Taking your medical history
  • Examining you and listening to your lungs
  • Performing spirometry, a lung function test

When these methods do not enable a clear diagnosis of asthma, the doctor may recommend a FeNO test. FeNO may also be used if spirometry cannot be used for some reason. It's important to note, though, that the FeNO test should only be used in people over the age of 5 years.

When is it used to help treat asthma?

FeNO testing can also be a useful tool to monitor asthma control and to help your doctor make decisions about treatment. These are reasons why your doctor might request regular FeNO testing for you to help with treatment:2

  • Your asthma is persistent and not well-controlled, even with inhaled steroids alone or with other medications.
  • You have symptoms that might require additional anti-inflammatory treatment methods.
  • You have an inherited risk for developing other allergic diseases, such as allergic rhinitis, asthma, and atopic dermatitis (eczema).
  • Your doctor wants formally evaluate your asthma control every 2 to 3 months.

Using the data from FeNO testing (along with other methods), your doctor can best prescribe and adjust your medication regime to keep your asthma under optimal control.

Are there any reasons not to use this test?

Well, as mentioned above, FeNO testing is not recommended for children under the age of 5 years. The reason for this is because it does not always correctly predict if repeated bouts of wheezing in such young children will actually turn into asthma down the road.2

Also, remember that FeNO testing alone is not to be used to:2

  • Diagnose asthma
  • Assess asthma control
  • Predict future flare-ups
  • Assess flare-up severity

It is a useful tool, but never the only tool. Indeed, it should only be considered part of an ongoing monitoring and management strategy for asthma treatment.

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This article represents the opinions, thoughts, and experiences of the author; none of this content has been paid for by any advertiser. The Asthma.net team does not recommend or endorse any products or treatments discussed herein. Learn more about how we maintain editorial integrity here.

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