Methods: Two hundred one patients aged 8 to 16 years with atopic asthma were recruited. Pulmonary function tests including BDR and FeNO were serially measured 10 times or more over 2 years when subjects were not receiving controller medications. After completion of monitoring, 1-year observation for loss of asthma control was performed.
Results: At least 1 positive BDR (≥12% improvement in FEV1 in response to inhaled short-acting b2-agonist) and high maximum FeNO (mFeNO) (≥ 35 parts per billion (ppb)) were confirmed over the 2-year observation period in 59% and 77% of study participants. There was no difference in FeNO levels between individuals with positive and negative BDRs. Risk of asthma control loss increased by 40% for patients with mFeNO ≥ 35 ppb [Hazard ratio (HR) = 1.94; P < 0.01], and by 26% for those with positive BDRs (HR = 1.40; P < 0.01). Risk of asthma control loss was greatest for patients with either (HR = 5.31; P < 0.01) or both positive BDRs and mFeNO ≥ 35 ppb (HR = 5.65; P< 0.01).
Conclusions: High FeNO was better able to predict upcoming loss of asthma control than BDRs, but use of both markers together provided a better indicator of asthma control loss.