Clinical implications of blood eosinophil count in patients with non-asthma–COPD overlap syndrome COPD

BACKGROUND Recent studies that assessed the relevance of the blood eosinophil count as a biomarker in patients with COPD may have overestimated it because they included patients with asthma-COPD overlap syndrome (ACOS). We investigated the clinical implications of the blood eosinophil count in patients with non-ACOS COPD. PATIENTS AND METHODS From a Korean COPD Subtype Study (KOCOSS) cohort, we selected patients with non-ACOS COPD after excluding ACOS patients according to Spanish criteria. Clinical characteristics and the incidence of moderate-to-severe exacerbation were compared among the four groups stratified according to the quartiles of blood eosinophil percent and count. RESULTS Of the KOCOSS cohort of 1,132 patients with COPD, 467 non-ACOS COPD patients (41.2%) with data of blood eosinophil count remained after excluding those with ACOS based on the Spanish definition. There was no difference in clinical characteristics among groups classified according to the quartiles of eosinophil percent and count. On multivariate logistic regression, eosinophil quartiles in percent and absolute count were not associated with the incidence of moderate-to-severe acute exacerbations of COPD (AECOPD). The eosinophil count did not affect the risk of AECOPD or forced expiratory volume in 1 second (FEV1) changes according to exposure to inhaled corticosteroid (ICS). However, by increasing the cutoff value for the eosinophil count from 200/μL to 600/μL, the odds ratio for risk of exacerbation increased serially from 0.82 to 2.96 on trend analysis. CONCLUSION In patients with non-ACOS COPD, the blood eosinophil count and percent were not associated with FEV1 changes, quality of life (QoL), AECOPD frequency, or response to ICS. The clinical implication of the blood eosinophil count should not be overestimated in patients with non-ACOS COPD.