Sputum eosinophilia
Kitaguchi et al. (26) studied patients with stable copD (FEv1 S80%) and asthmatic symptoms such as episodic breathlessness, wheezing, cough and chest tightness worsening at night or in the early morning (coPD with asthma group), in comparison with coPD patients without these symptoms (coPD without asthma group). They found that peripheral eosinophil counts and sputum eosinophil counts were significantly higher. A significant correlation was observed between the increase in FEvi in response to treatment with inhaled corticosteroids (ICS) and sputum eosinophil counts. Receiver operating characteristic curve analysis revealed 82.4% sensitivity and 84.8% specificity of sputum eosinophil count for detecting CoPD with asthma, using 2.5% as the cutoff value.