Blood eosinophil and neutrophil counts differentially identify frequent exacerbation in patients with COPD with physician-diagnosed asthma and COPD

Dear Editor, Patients presenting with clinical features of both asthma and COPD are categorized into a specific group called asthma-COPD overlap (ACO). A recent survey reported the prevalence of ACO to be 29.6% (95%CI: 19.3-39.9%) among patients with COPD. ACO is related to frequent exacerbation. However, useful biomarkers for predicting exacerbation in ACO patients remain under investigation. The aims of this study were (1) to investigate the clinical characteristics of ACO in Japanese patients and (2) to determine the differences between blood biomarkers predicting exacerbation between patients with COPD and those with ACO in a Japanese multicenter, 3-year observational cohort study (Keio COPD Comorbidity Research, K-CCR). For the purpose of this study, 393 COPD patients were included, while patients undergoing oral corticosteroid treatment were excluded (Supplementary Fig.1). Blood samples were collected at baseline at a time when the disease was stable. The definition of ACO was based on the diagnosis by a physician and/or by the affirmative response to the question; "Have you been ever told by your physician that you have asthma?".