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

Fractional exhaled nitric oxide (F ENO50 ), 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 ENO50 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 ENO50 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 ENO50 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 ENO50 patterns were observed by sex in later childhood and several factors were associated with either F ENO50 level or change in F ENO50 as participants aged. F ENO50 -age trajectories were similar by sex until age ∼11.5 years, after which males had greater F ENO50 change than females. This divergence in F ENO50 -age trajectories coincides with puberty. Males with higher starting BMI percentile had attenuated F ENO50 -age slopes. Among males, F ENO50 levels were lower in non-Hispanic white subjects. Among both sexes, participants with rhinitis had higher F ENO50 F ENO50 levels within individuals tracked over time; however, there was considerable variation in F ENO50 patterns across participants.F ENO50 trajectories from longitudinal data provide evidence of sex differences coinciding with puberty, suggesting potential hormone link. Improved understanding of determinants of F ENO50 trajectories is needed to realise the potential for using individualised predicted F ENO50 trajectories.