Passive smoking is a major determinant of exhaled nitric oxide levels in allergic asthmatic children

Background: Fraction of exhaled nitric oxide (FeNO), as a reflection of allergic bronchial inflammation, is considered to be a treatment follow-up parameter in allergic asthmatics. Factors such as active smoking can, however, influence FeNO measurement and are thus taken into account in the interpretation of this parameter. In children, the evidence in favor of an impact of passive smoking (PS) on FeNO measurement is controversial.

Objective: To evaluate the impact of PS on measurement of FeNO in allergic asthmatic children.

Methods: 70 non-treated allergic asthmatic children over the age of 5 years underwent phenotype characterisation by measurement of on-line FeNO, spirometry, and allergic tests (skin prick tests, total and specific IgE levels, blood eosinophilia). Children were considered to be exposed to PS when at least 5 cigarettes per day were declared by the family to be smoked at home.

Results: Mean FeNO in 48 children unexposed to PS was 62.3 ± 29.1 ppb versus 30.3 ±17.6 ppb in 22 exposed children (p<10^-4). A dose-response relation was observed between FeNO values and the number of cigarettes smoked at home (r = -0.41; p<10^-4). After adjustment for blood eosinophilia, age, allergenic sensitizations and asthma severity, multivariate analysis showed that PS exposure was negatively associated with FeNO (p<10^-4) and was the primary determinant of FeNO variations (PS alone accounted for 33% of FeNO variance).

Conclusion: Passive smoking is a major determinant of FeNO levels in non-treated allergic asthmatic children.

Clinical Implications: It would appear essential to take exposure to PS into account when interpreting FeNO results in this population.