Nitric oxide as a clinical guide for asthma management

Asthma is a pathologically heterogeneous disease, and the phenotype is characterized by different types of airway inflammation. Exhaled nitric oxide (F_ENO) measurements are a surrogate marker specific for eosinophilic airway inflammation. The latter is usually associated with steroid responsiveness, and hence, F_ENO may be used to guide steroid requirements in certain clinical situations. High F_ENO levels may be used to predict likely benefits with inhaled corticosteroid (ICS) therapy. Both high and low F_ENO levels are prognostically significant when withdrawal of ICS treatment is being considered. Studies have shown that, just as for induced sputum, repeated F_ENO measurements improve the cost-effectiveness of ICS therapy when used to guide dose requirements. In practice, F_ENO measurements are useful in the management of severe or difficult asthma. High and low F_ENO levels in symptomatic patients provide the clinician with information that enables active eosinophilic airway inflammation to be included or excluded. Either outcome is helpful in decision making. F_ENO measurements complement the use of other tests in asthma, but more work is required to determine reference values and cut-points for appropriate interpretation.

Key words: Asthma, exhaled nitric oxide, F_ENO, pulmonary function

Abbreviations used: F_ENO, Fraction of nitric oxide in exhaled air, ICS, Inhaled corticosteroid