Why it's done

The diagnosis of asthma is usually made using your medical history, a physical exam, and certain tests to see how well your lungs are working, such as peak flow measurement and spirometry tests. You may need tests that trigger and then treat mild asthma symptoms. These tests are called challenge tests.

Even after these tests, the diagnosis of asthma may still be uncertain, or there may be questions about the best treatment. In these cases the exhaled nitric oxide test may be helpful. Nitric oxide is produced throughout the body, including in the lungs, to fight inflammation and relax tight muscles. High levels of exhaled nitric oxide in your breath can mean that your airways are inflamed — one sign of asthma.

Nitric oxide testing is also done to help predict whether or not steroid medications, which decrease inflammation, are likely to be helpful for your asthma. If you've already been diagnosed with asthma and treated with one of the steroid medications, your doctor may use an exhaled nitric oxide test during office visits to help determine whether your asthma is under control.

Exhaled nitric oxide testing may not be necessary or provide useful information for everyone who has asthma. In addition, it may not be available in all hospitals or doctor's offices.

June 24, 2017
References
  1. Dweik RA, et al. An official ATS clinical practice guideline: Interpretation of exhaled nitric oxide levels (FENO) for clinical applications. American Journal of Respiratory and Critical Care Medicine. 2011;184:602.
  2. Dweik RA. Exhaled nitric oxide analysis and applications. http://www.uptodate.com/home. Accessed Oct. 17, 2016.
  3. Mummadi SR, et al. Update on exhaled nitric oxide in clinical practice. Chest. 2016;149:1340.
  4. Essat M, et al. Fractional exhaled nitric oxide for the management of asthma in adults: A systematic review. European Respiratory Journal. 2016;47:751.
  5. Calhoun KH. The role of fractional exhaled nitric oxide in asthma management. Otolaryngology Clinics of North America. 2014;47:87.
  6. Li JT (expert opinion). Mayo Clinic, Rochester, Minn. Nov. 7, 2016.