High FENO levels are defined as:

Depending on the results of the physical examination and other clinical tests, atopic asthma should be considered. As the high FENO levels signify eosinophilic inflammation, the patient is likely to respond to inhaled or oral steroids.

In children, high values can confirm the diagnosis of asthma if objective reversible evidence of airway obstruction is present. Read more on reversibility testing here.

If the patient is symptomatic and on anti-inflammatory therapy, consider: [Taylor 2006]

• Check compliance

• Review inhalation technique
- If the patient is a child, consider using metered dose inhaler and spacer if he or she is currently using a dry powdered device

• Consider that they may be:
- exposed to high levels of allergens
- about to relapse or experience an exacerbation
- steroid resistance (this is rare)

If the patient is asymptomatic and on anti-inflammatory therapy: [Taylor 2006]

• No change in treatment if patient is stable