Clinical utility of exhaled nitric oxide fraction in the management of asthma and COPD

Exhaled nitric oxide fraction (F(ENO)) values can be easily measured using portable analysers and are a surrogate marker of airway eosinophilia. F(ENO) may be useful in diagnosing and monitoring conditions characterised by airway eosinophilia, i.e. asthma and possibly COPD. Many factors other than asthma and COPD affect F(ENO), especially atopy, which is associated with elevated F(ENO). One guideline recommends that F(ENO) should be used as part of the diagnostic pathway for asthma diagnosis in adults and children aged >5 years. The role of F(ENO) in monitoring asthma is even less clear, and most guidelines do not recommend its use outside of specialist asthma clinics. Currently, F(ENO) is not recommended for diagnosis or monitoring of COPD. Although F(ENO) is starting to find a place in the management of asthma in children and adults, considerably more research is required before the potential of F(ENO) as an objective measurement in asthma and COPD can be realised. KEY POINTS: For individuals aged ≥12 years, F(ENO) is not recommended by all guidelines as a test to diagnose asthma (recommended only by the UK National Institute for Health and Care Excellence guideline for asthma symptoms, which are likely to respond to corticosteroid treatment). F(ENO) may be used in conjunction with other investigations to diagnose asthma in 5–16-year-olds where there is diagnostic uncertainty, but further evidence is required. F(ENO) is not recommended as a routine test to monitor all patients with asthma or to titrate asthma treatment. F(ENO) is not recommended for routine clinical testing in adults with COPD. F(ENO) may be useful to identify patients with COPD who could benefit from the use of inhaled corticosteroids (asthma–COPD overlap). EDUCATIONAL AIMS: To understand what factors other than asthma and COPD affect F(ENO.) To understand the current controversies in the application of F(ENO) to diagnosis and management of asthma in children. To understand the current controversies in the application of F(ENO) to diagnosis and management of asthma and COPD in adults.