Objectives: The relationship between exhaled nitric oxide (FeNO) and asthma severity or control is inconsistent. Active smoking lowers FeNO, but the relationship between passive smoking and FeNO is less clear. Children may be exposed to low-level environmental tobacco smoke (ETS) or thirdhand smoke, even if parents avoid smoking in the presence of their children. Our hypothesis was that FeNO is lower in children with asthma exposed to low-level ETS when compared with those who are not exposed.
Methods: Children with stable asthma, 8-18 years of age, on low- or medium-dose inhaled corticosteroids (ICS) were enrolled. Spirometry, Asthma Control Questionnaire (ACQ), FeNO, exhaled breath condensate pH (EBC pH), and EBC ammonia were compared between children with and without ETS exposure as determined by urinary cotinine.
Results: Thirty-three subjects were enrolled, of which 10 (30%) had urinary cotinine levels ≥1 ng/ml. There were no significant differences between the two groups in age, sex, BMI percentile, atopy status, FEV(1), EBC pH, or EBC ammonia. Median ACQ was 0.29 (IQR: 0.22-0.57) for those with cotinine levels <1 ng/ml and 0.64 (IQR: 0.57-1.1) for those with cotinine levels of ≥1 ng/ml, p = .02. Median FeNO (ppb) was 23.9 (IQR: 15.2-34.5) for unexposed subjects and 9.6 (IQR: 5.1-15.8) for exposed subjects, p = .008.
Conclusions: Children with asthma on low to medium doses of ICS and recent low-level ETS exposure have lower FeNO levels when compared with non-ETS-exposed subjects. Exposure to low-level ETS or thirdhand smoke may be an important variable to consider when interpreting FeNO as a biomarker for airway inflammation.