The association of blood eosinophil counts and FEV1decline: a cohort study

Background Accelerated lung function decline is characteristic of chronic obstructive pulmonary disease (COPD). However, the association between blood eosinophil counts and lung function decline, accounting for current smoking status, in young individuals without prevalent lung disease is not fully understood. Methods This is a cohort study of 629 784 Korean adults without COPD or a history of asthma at baseline who participated in health screening examinations including spirometry and differential white blood cell counts. We used linear mixed effects model to estimate the annual change in FEV 1 (mL) by baseline blood eosinophil count, adjusting for covariates including smoking status. We also performed a stratified analysis by baseline and time-varying smoking status. Results During a mean follow-up of 6.5 years (maximum of 17.8 years), the annual change in FEV 1 (95% confidence interval [CI]) in participants with eosinophil counts <100, 100–199, 200–299, 300–499, and ≥500 cells/µL in the fully adjusted model were −23.3 (−23.9, −22.7), −24.3 (−24.9, −23.7), −24.8 (−25.5, −24.2), −25.5 (−26.2, −24.8), and −26.8 (−27.7, −25.9) mL, respectively. When stratified by smoking status, participants with higher eosinophil count had a faster decline in FEV 1 than those with lower eosinophil count in both never- and ever-smokers, which persisted when time-varying smoking status was used. Conclusions Blood eosinophil counts were associated with a faster lung function decline among healthy individuals without lung disease, independent of smoking status. The findings suggest that blood eosinophil counts contribute to the risk of faster lung function decline, particularly among younger adults without a history of lung disease.