The association between blood eosinophil count and clinical outcomes during inhaled corticosteroid/long-acting β2-agonist treatment in stable-phase chronic obstructive pulmonary disease: A retrospective cohort analysis

Blood eosinophil (EOS) count has emerged as a potential biomarker associated with inhaled corticosteroid (ICS) responsiveness in chronic obstructive pulmonary disease (COPD). However, the relationship between EOS counts and clinical outcomes during ICS treatment in stable-phase COPD remains unclear. This study aimed to evaluate the association between baseline EOS counts and changes in lung function, symptom burden, and exacerbation frequency during ICS/long-acting β ₂ -agonist (LABA) treatment. A retrospective cohort study included 200 stable-phase COPD patients treated with ICS/LABA combinations for 12 months. Participants were stratified into low (<150 cells/μL), medium (150–300 cells/μL), and high (>300 cells/μL) EOS groups. Outcomes included changes in forced expiratory volume in 1 second (FEV1%pred), COPD Assessment Test scores, 6-minute walk distance, and annualized exacerbation rates. Inflammatory markers (interleukin-5 [IL-5], eosinophil cationic protein) were analyzed. Baseline EOS counts were positively correlated with IL-5 and eosinophil cationic protein. After 12 months, higher baseline EOS counts were associated with greater changes in FEV1%pred and 6-minute walk distance. The reduction in exacerbation rates was 51.9% in the high EOS group versus 22.3% in the low EOS group. Receiver operating characteristic analysis identified a baseline EOS cutoff of 285 cells/μL for predicting FEV1%pred improvement ≥5%. Higher baseline EOS counts are associated with greater improvements in clinical outcomes during ICS/LABA therapy in stable COPD, although the absence of a non-ICS comparator precludes causal inference. These findings support further investigation of EOS-guided treatment strategies in this population.