The fractional concentration of Nitric Oxide in the exhaled air (FeNO) is a moderately promising biomarker of type-2 airway inflammation, and its measurement is also feasible in children. The available evidence is still not enough to support the routine use of FeNO to diagnose or manage asthma in every patient in clinical practice. However, its role in identifying asthma with eosinophilic inflammation is of particular interest in managing severe asthma.

FeNO levels increase with age and height in healthy subjects, particularly in males, and are also influenced by ethnicity. FeNO measurement can support asthma diagnosis and help predict asthma development later in life in young children with recurrent wheezing. FeNO-guided asthma management effectively reduces asthma exacerbations but may result in a higher daily dose of inhaled corticosteroids. FeNO can also be used as a marker to evaluate adherence to asthma treatment and predict response to different biologicals, especially Omalizumab and Dupilumab.

This review outlines recent data on the application of FeNO in childhood-onset asthma diagnosis and management and phenotyping subjects with severe asthma who may benefit from monoclonal antibody administration.