Tobacco smoke exposure and fractional exhaled nitric oxide levels among US adolescents

Background: Fractional exhaled nitric oxide (FeNO) can objectively guide clinical practice in the assessment, diagnosis, and treatment of eosinophilic airway inflammation. FeNO values may be affected by current smoking, but the role of tobacco smoke exposure (TSE) is understudied. Objective: This study investigated the associations between biochemically validated and self-reported TSE and FeNO levels among U.S. nonsmoking adolescents without asthma. Methods: National Health and Nutrition Examination Survey 2007-2012 data were used. TSE was assessed via serum cotinine and self-reported measures. We assessed FeNO continuously and using cutpoints of >35 ppb and >50 ppb to indicate likely eosinophilic inflammation in children and adults, respectively. We conducted linear and logistic regression adjusting for potential covariates. Results: Overall, 34.0% of adolescents had low cotinine (0.05-2.99 ng/ml), 6.2% had high cotinine (>= 3.00 ng/ ml), and 11.9% had home TSE. Compared to adolescents with no/minimal cotinine, adolescents with high cotinine were at reduced odds to have FeNO >35 ppb (adjusted odds ratio [aOR] = 0.54, 95%CI = 0.43,0.69). Adolescents with low cotinine had lower FeNO values (beta = -2.05, 95%CI = -3.61,-0.49), and were also at decreased odds to have FeNO >35 ppb (aOR = 0.74, 95%CI = 0.66,0.83) and FeNO >50 ppb (aOR = 0.62, 95% CI = 0.53,0.72). Adolescents with home TSE were at reduced odds to have FeNO >50 ppb (aOR = 0.72, 95%CI = 0.57,0.91) than adolescents without home TSE. Adolescents with a higher number of cigarettes/day smoked inside their home were at reduced odds to have FeNO >35 ppb (OR = 0.98, 95%CI = 0.97,0.99) and FeNO >50 ppb (OR = 0.98, 95%CI = 0.96,0.99). Conclusions: TSE was associated with decreased FeNO levels. The addition of TSE may be clinically important when interpreting thresholds for FeNO.