Exhaled nitric oxide in asthma: from diagnosis to management

Purpose of review Exhaled nitric oxide (F E NO) is a noninvasive marker of eosinophilic airway inflammation, therefore, highly informative in asthma. Although F E NO measurement is a potentially accessible tool to many physicians, recommendations regarding its clinical utility in diagnosing or tailoring treatment have not reached the expected diffusion. More recently F E NO emerged as a biomarker for type-2 asthma phenotyping and a predictor of response to biologics. Recent findings The physiological discoveries and relevant acquisitions in clinical practice regarding F E NO in asthma are presented. The F E NO story draw a wavy path, characterized by promising findings, exciting confirmations and periods of low visibility. F E NO emerged as a tool to increase the probability of asthma diagnosis. F E NO predicts response to inhaled glucocorticoids (ICS), favoring the development of tailored treatment strategies and unrevealing nonadherence to ICS in difficult-to-treat or uncontrolled asthma. Finally, F E NO was associated with a more severe phenotype and became a consolidated biomarker of type-2 inflammation. Summary F E NO demonstrated to be a noninvasive and very reproducible test, encompassing many applications in the field of asthma management. Its routinely use, according to international guidelines, may improve the quality of patient assistance, from difficult-to-treat cases to biologic monitoring.