The interpretation of exhaled nitric oxide values in children with asthma depends on the degree of bronchoconstriction and the levels of asthma severity.

Background: The clinical implications of fractional exhaled nitric oxide (F(ENO)) measurements in childhood asthma are unclear. We aimed to evaluate the relationship between the level of exhaled nitric oxide and pre-bronchodilator FEV1 and the change in FEV1 after bronchodilator in children with asthma.

Methods: This was a retrospective, cross-sectional study. We evaluated data from medical documentation of children with asthma with special attention to F(ENO) results, asthma severity, FEV1 (% predicted), and bronchial reversibility test.

Results: Four hundred and five subjects (age 6-18 y) completed the study. Median levels of F(ENO) increased linearly with subjects' age (P = .03). We found a nonlinear trend of pre-bronchodilator FEV1 across 4 quartiles of F(ENO) in episodic and mild asthma; we observed lower pre-bronchodilator FEV1 in children with higher F(ENO), but only up to the F(ENO) value of 35.4 ppb; in children with F(ENO) value > 35.4 ppb, pre-bronchodilator FEV1 was increased. We found a linear increasing trend of change from baseline (after 400 μg of salbutamol) in FEV1 across F(ENO) categories in children with moderate asthma.

Conclusions: Our results suggest a need to measure F(ENO) before as well as after spirometry. Consequently, in children with asthma with bronchial obstruction, we suggest assessing F(ENO) after short-acting β2 agonists as well. (ClinicalTrials.gov registration NCT00815984.).