Patterns and determinants of exhaled nitric oxide trajectories in schoolchildren over a 7-year period

Fractional exhaled nitric oxide (F _ENO ), a marker of allergic airway inflammation, is used in respiratory research and asthma clinical care; however, its trajectory with increasing age during childhood has not been well characterised. We examined F _ENO longitudinally during a period of important somatic growth to describe trajectories across childhood and adolescence in healthy participants and evaluate clinical factors as potential determinants of trajectories.F _ENO was collected at six visits over 8 years in a population-based cohort of 1791 schoolchildren without asthma (median age at entry 8.4 years). Smooth sex-specific F _ENO trajectories were estimated using generalised additive mixed models, with participant-level random effects. We evaluated whether sex-specific trajectories were influenced by race/ethnicity, body mass index (BMI) percentile, allergic rhinitis or puberty.Different F _ENO patterns were observed by sex in later childhood and several factors were associated with either F _ENO level or change in F _ENO as participants aged. F _ENO -age trajectories were similar by sex until age ∼11.5 years, after which males had greater F _ENO change than females. This divergence in F _ENO -age trajectories coincides with puberty. Males with higher starting BMI percentile had attenuated F _ENO -age slopes. Among males, F _ENO levels were lower in non-Hispanic white subjects. Among both sexes, participants with rhinitis had higher F _ENO F _ENO levels within individuals tracked over time; however, there was considerable variation in F _ENO patterns across participants.F _ENO trajectories from longitudinal data provide evidence of sex differences coinciding with puberty, suggesting potential hormone link. Improved understanding of determinants of F _ENO trajectories is needed to realise the potential for using individualised predicted F _ENO trajectories.