The change in exhaled nitric oxide in adolescents – a longitudinal cohort study

Abstract

Background: Predictive equations for fractional exhaled nitric oxide (FeNO) have been developed for adults, but the patterns through adolescence are poorly described. We describe the longitudinal changes of FeNO and the associations with predictors during adolescence.

Method: Children recruited into the Manchester Asthma and Allergy Study were followed up at the age of 8, 11, 16 and 18 years. Validated questionnaires were interviewer-administered. Children were skin prick tested (SPT) for common aeroallergens and FeNO was measured.

Results: Of 1184 children, 603 (50% boys, 95% Caucasian) had two or more FeNO measurements. FeNO were higher in children with current wheeze, history of physician-diagnosed asthma and SPT sensitisation in all age groups (p<0.001). Amongst healthy non-atopic (NA) children, the FeNO geometric mean (95th percentile) were 8.6 (16.4), 8.6 (16.6), 13.5 (32.6) and 12.0 (26.4) ppb at 8, 11, 16 and 18 years, respectively. In univariate mixed linear regression equations in NA children, log (FeNO) was associated with age (β=0.019, p<0.001), height (β=0.004, p<0.001), weight (β=0.004, p<0.001), but not gender (p=0.98). Pubertal stage did not predict FeNO. There were significant age*gender and age*height interactions (p<0.001), suggesting that the effects of gender and height depends on age. In cross sectional analysis, gender and height started to show associations with FeNO from 18 years but not before.

Conclusion: The predictors of FeNO appear to differ in children from adults. If FeNO is to be used in asthma diagnosis, predictive equations need to be established in children as well as adults. This finding requires further investigation.