Relationship between exhaled NO, respiratory symptoms, lung function, bronchial hyperresponsiveness, and blood eosinophilia in school children

Background: Exhaled nitric oxide (eNO) may serve as a non-invasive marker of airway inflammation but its relationship with other commonly used measures has not been evaluated. Methods: Levels of eNO in a sample of 450 children aged 7-12 years out of a total sample of 2504 school children living in different urban areas near motorways were determined. The aim of this cross-sectional study was to explore the relationship between eNO, impairment of lung function (PEF, FVC, FEV₁ and MMEF), bronchial hyperresponsiveness (BHR), and blood eosinophilia in children with and without atopy as assessed by skin prick testing. Results: Regression analysis showed that wheezing and nasal discharge and conjunctivitis that had occurred during the previous 12 months were positively associated with eNO levels in atopic children (relative increase of 1.48 and 1.41, respectively; p<0.05) but not in non-atopic children. Similarly, BHR and the number of blood eosinophils per ml were positively associated with eNO levels in atopic children (relative increase of 1.55 and 2.29, respectively; p<0.05) but not in non-atopic children. The lung function indices PEF, FVC, FEV₁ and MMEF were not associated with eNO levels. Conclusions: In addition to conventional lung function tests and symptom questionnaires, eNO is a suitable measure of airway inflammation and its application may reinforce the power of epidemiological surveys on respiratory health.