RATIONALE: Whether high blood eosinophils are associated with COPD exacerbations among individuals with COPD in the general population is largely unknown.

OBJECTIVES: To test the hypothesis that high blood eosinophils predict COPD exacerbations.

METHODS: Among 81,668 individuals from the Copenhagen General Population Study, we examined 7,225 with COPD based on spirometry. We recorded blood eosinophils at baseline and future COPD exacerbations longitudinally, defined as moderate (short-course treatment of systemic corticosteroids) or severe (hospitalization). We also assessed exacerbation risk in a subgroup of 203 COPD individuals with clinical COPD, defined as participants with ≥ 10 pack-years, FEV1 < 70% of predicted value and ≥ 1 moderate or severe exacerbation in the year prior to baseline.

MEASUREMENTS AND MAIN RESULTS: During a median of 3.3 years of follow-up (range 0.03-8.1), 1,439 severe and 2,864 moderate COPD exacerbations were recorded. Among all participants with COPD, blood eosinophils above versus below 0.34∙10(9) cells/L had a multivariable adjusted incidence rate ratio of 1.76 (95%CI: 1.56-1.99) for severe exacerbations and of 1.15 (1.05-1.27) for moderate exacerbations. Corresponding values in those with clinical COPD were 3.21 (2.49-4.14) and 1.69 (1.40-2.04). In contrast, using a cut-point of 2% for blood eosinophils, the risk of exacerbations was only increased for severe exacerbations among individuals with clinical COPD but not in individuals from the broader population.

CONCLUSIONS: Among individuals with COPD in the general population, increased blood eosinophil levels above 0.34∙10(9) cells/L were associated with a 1.76-fold increased risk of severe exacerbations.