Exhaled Nitric Oxide Predicts Eosinophilic Airway Inflammation in COPD

Purpose Chronic obstructive pulmonary disease (COPD) with eosinophilic airway inflammation may represent a unique phenotype, possibly with shared features of COPD and asthma. The role of exhaled nitric oxide (eNO) in identifying COPD patients with sputum eosinophilia was examined in this study. Methods Ninety COPD patients without past medical history of asthma or allergic diseases were prospectively enrolled, and their eNO, lung function, and cellular profile of induced sputum were measured. Eosinophil cationic protein and IgE in sputum and venous blood also were determined. Subjects with and without sputum eosinophilia (>3 %) were compared. The role of eNO in the prediction of sputum eosinophilia was assessed in a logistic regression model. Results Patients with sputum eosinophilia had significantly higher levels of eNO (29 vs. 18 ppb, p = 0.01) than those without. The difference in serum total IgE (168 vs. 84.9 IU/ml, p = 0.057) and percentages of positive allergen test results (48.3 vs. 29.5 %, p = 0.082) showed a trend toward significance. The sputum eosinophil level was significantly correlated to the eNO level ( r = 0.485, p 23.5 ppb) in the prediction of sputum eosinophilia were 3.909 (confidence interval (CI) 1.542–9.91, p = 0.004) and 4.329 (CI 1.306–14.356, p = 0.017), respectively. Conclusions eNO is a good marker to identify COPD patients with eosinophilic airway inflammation.