Background: Exhaled nitric oxide (FE_NO) is raised in asthmatic children, but there are inconsistencies in the relationship between FE_NO and characteristics of asthma, including atopy, increased airway responsiveness (AR), and airway inflammation. The aim of this study was to investigate the relationship between FE_NO and asthma, atopy, and increased AR in children.

Methods: One hundred and fifty five children (79 boys) of mean age 11.5 years underwent an assessment that included FE_NO measurements, spirometric tests, inhaled histamine challenge, and a skin prick test. Blood was collected for eosinophil count. Current and past asthma like symptoms were determined by questionnaire.

Results: In multiple linear regression analyses FE_NO was associated with atopy (p<0.001), level of AR (p = 0.005), blood eosinophil count (p = 0.007), and height (p = 0.002) but not with physician diagnosed asthma (p = 0.1) or reported wheeze in the last 12 months (p = 0.5). Separate regression models were conducted for atopic and non-atopic children and associations between FE_NO and AR, blood eosinophils and height were only evident in atopic children. Exhaled NO was raised in children with a combination of atopy and increased AR independent of symptoms.

Conclusion: Raised FE_NO seems to be associated with an underlying mechanism linking atopy and AR but not necessarily respiratory symptoms.