Methods: We examined the datasets of elderly asthma and non-asthmatic chronic cough recruited from previously established cohorts. The inclusion criteria were as follows: 1) elderly subjects (≥65 years old), 2) no current oral or inhaled corticosteroids and 3) no significant comorbidities. Sputum eosinophilia was defined as induced sputum eosinophils≥3%. The diagnostic utility was assessed using receiver operating curve (ROC) analyses for blood eosinophils in predicting sputum eosinophilia.
Results: A total of 74 elderly asthma and 75 non-asthmatic chronic cough patients were analyzed. There were no significant difference in their demographic profiles (age, gender and smoking) between two groups. Of them, 59 elderly asthma and 45 non-asthmatic chronic cough patients had sputum eosinophilia. In Spearman tests, the correlations between blood eosinophils% and sputum eosinophil% were significant in eosinophilic asthma (r=0.577, p<0.001) but not in non-asthmatic eosinophilic bronchitis (r=0.019, p=0.870). In ROC analyses for sputum eosinophilia, blood eosinophils showed a moderate utility (the area under the ROC curve [AUC] 0.838) in asthma, but no utility (AUC 0.489) in non-asthmatic chronic cough.
Conclusions: Unlike asthma, blood eosinophils did not have any diagnostic utility for sputum eosinophilia in non-asthmatic chronic cough. These findings could suggest a different pathophysiology in airway eosinophilic inflammation between two entities.