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 (FEV₁) were performed using random mixed-effects regression models with adjustments for demographics, smoking, baseline FEV₁, 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 FEV₁ 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 FEV₁ 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.