Exhaled nitric oxide as a marker of asthma control in smoking patients

Exhaled nitric oxide fraction (F(eNO)), which is a reliable marker of eosinophilic airway inflammation, is partially suppressed by tobacco smoking. Consequently, its potential as a biomarker in asthma management has never been evaluated in smoking patients. In the present study, the authors tested the validity of F(eNO) to predict asthma control in this population. F(eNO) and the Asthma Control Questionnaire (ACQ) were recorded at least once in 411 nonsmoking (345 with at least two visits) and 59 smoking (51 with at least two visits) asthma patients. Despite similar mean ACQ scores (1.5 versus 1.7), F(eNO) was reduced in smoking asthmatics (18.1 ppb versus 33.7 ppb). A decrease in F(eNO) of <20% precludes asthma control improvement in nonsmoking (negative predictive value (NPV) 78%) and in smoking patients (NPV 72%). An increase in F(eNO) <30% is unlikely to be associated with deterioration in asthma control in both groups of patients (NPV = 86% and 84% in nonsmoking and smoking patients, respectively). It is concluded that, even in smokers, sequential changes in F(eNO) have a relationship with asthma control. The present study is the first to indicate that cigarette smoking does not obviate the clinical value of measuring F(eNO) in asthma among smokers.