High eosinophil counts predict decline in FEV1: results from the CanCOLD study

Introduction The aim of this study was to examine the association between blood eosinophil levels and the decline in lung function in individuals aged >40 years from the general population. Methods The study evaluated the eosinophil counts from thawed blood in 1120 participants (mean age 65 years) from the prospective population-based Canadian Cohort of Obstructive Lung Disease (CanCOLD) study. Participants answered interviewer-administered respiratory questionnaires and performed pre-/post-bronchodilator spirometric tests at 18-month intervals; computed tomography (CT) imaging was performed at baseline. Statistical analyses to describe the relationship between eosinophil levels and decline in forced expiratory volume in 1 s (FEV 1 ) were performed using random mixed-effects regression models with adjustments for demographics, smoking, baseline FEV 1 , ever-asthma and history of exacerbations in the previous 12 months. CT measurements were compared between eosinophil subgroups using ANOVA. Results Participants who had a peripheral eosinophil count of ≥300 cells·µL −1 (n=273) had a greater decline in FEV 1 compared with those with eosinophil counts of <150 cells·µL −1 (n=430; p=0.003) (reference group) and 150–<300 cells·µL −1 (n=417; p=0.003). The absolute change in FEV 1 was −32.99 mL·year −1 for participants with eosinophil counts <150 cells·µL −1 ; −38.78 mL·year −1 for those with 150–<300 cells·µL −1 and −67.30 mL·year −1 for participants with ≥300 cells·µL −1 . In COPD, higher eosinophil count was associated with quantitative CT measurements reflecting both small and large airway abnormalities. Conclusion A blood eosinophil count of ≥300 cells·µL −1 is an independent risk factor for accelerated lung function decline in older adults and is related to undetected structural airway abnormalities.