Study Background and Disease Burden
Fractional exhaled nitric oxide (FeNO) is a recognized biomarker used widely in clinical practice to aid in the diagnosis, phenotyping, and management of asthma. It serves as a non-invasive marker of eosinophilic airway inflammation, which is characteristic of certain asthma phenotypes. However, interpreting FeNO values in clinical practice requires accurate knowledge of normal reference ranges, especially as values may vary with age, sex, and physiological as well as environmental factors. While FeNO thresholds have been proposed, existing data primarily come from patient populations or limited age groups; comprehensive reference data spanning the lifespan in respiratory healthy, non-smoker, non-atopic individuals remain sparse. This knowledge gap hinders the precise clinical application of FeNO testing across diverse patient demographics and risk profiles. Understanding normal FeNO values and their determinants across the lifespan is critical to improve diagnostic accuracy, personalize treatment, and prevent misclassification in asthma and other airway inflammatory diseases.
