Longitudinal Relationship between Sputum Eosinophils and Exhaled Nitric Oxide in Children with Asthma

To the Editor: Measurement of fraction of exhaled nitric oxide (FeNO) is an established tool for the assessment of airway inflammation in asthma. Despite increasing evidence of a poor relationship between the two (1), FeNO continues to be widely regarded as a surrogate marker of sputum eosinophilia (2–4). Furthermore, recent American Thoracic Society (ATS) guidelines have suggested clinically significant cut points for low and high FeNO...