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
  • Results of other tests, such as peak flow tests or spirometry tests
  • Past nitric oxide test results
  • 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
Mar. 19, 2014