Results

Higher than normal levels of exhaled nitric oxide generally mean your airways are inflamed — a sign of asthma.

  • Levels under about 20 parts per billion in children and under about 25 parts per billion in adults are considered normal.
  • More than 35 parts per billion in children and 50 parts per billion in adults may signal airway inflammation caused by asthma.

Nitric oxide test results can vary widely from person to person. When interpreting test results, your doctor will consider a number of other factors. These may include:

  • Your asthma signs and symptoms
  • Past nitric oxide test results
  • Results of other tests, such as peak flow tests or spirometry tests
  • Medications you take
  • Whether you have a cold or the flu
  • Whether you have hay fever or other allergies
  • Whether or not you smoke
  • Your age
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.

Nitric oxide test for asthma