Blood eosinophil level and lung function trajectories: cross-sectional and longitudinal studies in European cohorts

Elevated blood eosinophils have been associated with lower lung function and are believed to be associated with accelerated lung function decline.

Blood eosinophils were measured in four cohorts: <45 years cohort within the Vlagtwedde-Vlaardingen (V&V) study, the Uppsala cohort of the European Community Respiratory Health Survey (ECRHS-Uppsala; <45 years), ≥45 years cohort within the V&V study, and the Rotterdam study (≥45 years). Blood eosinophils at baseline were classified as normal (<300 cells·μL^-1) or elevated (≥300 cells·μL^-1). Lung function was measured at baseline and follow-up with spirometry: forced expiratory volume in 1 s (FEV₁), vital capacity (VC) and their ratio FEV₁/VC. The association between blood eosinophils and lung function was tested cross-sectionally using linear regression and longitudinally using a mixed model, both adjusted for age, sex, height, pack-years smoking and smoking status. Stratified analyses were done for asthma.

Elevated blood eosinophils were associated with lower FEV₁ (regression coefficient -147 mL (95% CI -188 to -105 mL)), VC (-120 mL (-165 to -75 mL)) and FEV₁/VC (-1.3% (-1.9% to -0.6%)) at baseline in the two <45 years cohorts, and with lower FEV₁ (-70 mL (-112 to -27 mL)) and FEV₁/VC (-1.8% (-2.6% to -1.0%)) in the two ≥45 years cohorts. Elevated blood eosinophils were associated with an accelerated decline in FEV₁ (-5.5 mL·year^-1 (95% CI -10.5 to -0.5 mL·year^-1)) and VC (-6.4 mL·year^-1 (-11.26 to -1.5 mL·year^-1)) compared to normal blood eosinophils in the younger asthmatic subjects in the longitudinal studies.

Elevated blood eosinophils are associated with lower lung function in the general population and with an accelerated lung function decline among asthmatic individuals.