Prevalence of persistent blood eosinophilia: relation to outcomes in patients with COPD

The impact of blood eosinophilia in chronic obstructive pulmonary disease (COPD) remains controversial. To evaluate the prevalence and stability of a high level of blood eosinophils (>= 300 cells.mu L-1) and its relationship to outcomes, we determined blood eosinophils at baseline and over 2 years in 424 COPD patients (forced expiratory volume in 1 s (FEV1) 60% predicted) and 67 smokers without COPD from the CHAIN cohort, and in 308 COPD patients (FEV1 60% predicted) in the BODE cohort. We related eosinophil levels to exacerbations and survival using Cox hazard analysis. In COPD patients, 15.8% in the CHAIN cohort and 12.3% in the BODE cohort had persistently elevated blood eosinophils at all three visits. A significant proportion (43.8%) of patients had counts that oscillated above and below the cut-off points, while the rest had persistent eosinophil levels <300 cells.mu L-1. A similar eosinophil blood pattern was observed in controls. Exacerbation rates did not differ in patients with and without eosinophilia. All-cause mortality was lower in patients with high eosinophils compared with those with values <300 cells.mu L-1 (15.8% versus 33.7%; p=0.026). In patients with COPD, blood eosinophils >= 300 cells.mu L-1 persisting over 2 years was not a risk factor for COPD exacerbations. High eosinophil count was associated with better survival.