Elevated exhaled nitric oxide in adolescents relates to incident allergic symptoms: a prospective cohort study.

BACKGROUND: The fraction of exhaled nitric oxide (FeNO) is a marker of type-2 inflammation in the airways and elevated FeNO may precede development of allergic disease. The aim of the present study was to investigate the association between elevated FeNO and the development of allergic symptoms.

METHODS: A total of 959 adolescents from a general population answered, together with their parents, a standardized questionnaire, performed lung function and FeNO measurements at a baseline visit. Four years later, 921 of these subjects (96%) completed a to a great extent same version of the baseline questionnaire.

RESULTS: Adolescents with self-reported incident allergic symptoms to cat (n = 50) or dog (n = 33) had higher baseline FeNO (p < 0.001) than subjects without allergic symptoms to cat and dog at either time point (n = 776 and n = 838, respectively). Adolescents with incident allergic symptoms to pollen did not have elevated baseline FeNO. The adjusted odds ratio [aOR (95% confidence interval)] for incident allergic symptoms to cat was 4.2 (2.2, 8.0) times higher if FeNO was > 75th percentile (vs. < 75th percentile) at baseline. This was consistent after exclusion of subjects with reported asthma, wheeze or rhinitis at baseline [aOR (95% CI) 8.6 (3.0, 24.1)].

CONCLUSIONS: Elevated FeNO in adolescents related to an increased risk of developing allergic symptoms to cat and dog, but not pollen allergens, within four years.