Purpose of review: This review focuses on the most recent studies investigating fractional nitric oxide concentration in exhaled breath (FeNO) as a useful biomarker for identifying specific phenotypes in asthma and as a tool for asthma diagnosis, monitoring and clinical decision-making.
Recent findings: On the basis of the current literature, it has been highlighted that FeNO is a clinically relevant marker in various clinical aspects of asthma: FeNO is a predictor for developing asthma in persistent rhinitis or in infants with respiratory symptoms; FeNO contributes to identification of asthma phenotypes in both children and adults, also in relation to severity; FeNO is useful in monitoring the effectiveness of inhaled corticosteroids (including compliance) and biologic treatments like omalizumab; FeNO, in conjunction with symptom registration and lung function measurements, contributes to asthma diagnosis and optimizes asthma management.
Summary: FeNO provides further information in distinguishing different phenotypes in asthma, allowing a much more appropriate control of the disease, especially in patients with difficult/severe asthma. In the future, it would be interesting to shed light on the hidden biological mechanisms responsible for low or normal FeNO values in symptomatic asthmatic patients.