Blood eosinophil counts and the development of obstructive lung disease: the Kangbuk Samsung Health Study

The impact of blood eosinophil counts on the development of chronic obstructive lung disease (COPD) is unknown. We investigated whether a higher blood eosinophil count was associated with the risk of developing obstructive lung disease (OLD) in a large cohort of men and women free from lung disease at baseline.This was a cohort study of 359 456 Korean adults without a history of asthma and without OLD at baseline who participated in health screening examinations including spirometry. OLD was defined as pre-bronchodilator forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) <0.7 and FEV1 <80% predicted.After a median (interquartile range) follow-up of 5.6 (2.9-9.2) years, 5008 participants developed incident OLD (incidence rate 2.1 (95% CI 2.1-2.2) per 1000 person-years). In the fully adjusted model, the hazard ratios for incident OLD comparing eosinophil counts of 100- <200, 200- <300, 300- <500 and ≥500 versus <100 cells·μL-1 were 1.07 (95% CI 1.00-1.15), 1.30 (95% CI 1.20-1.42), 1.46 (95% CI 1.33-1.60) and 1.72 (95% CI 1.51-1.95), respectively (ptrend<0.001). These associations were consistent in clinically relevant subgroups, including never-, ex- and current smokers.In this large longitudinal cohort study, blood eosinophil counts were positively associated with the risk of developing of OLD. Our findings indicate a potential role of the eosinophil count as an independent risk factor for developing COPD.