Blood eosinophilia and the number of exacerbations in COPD patients

Abstract

Background: There are limited data on the relevance of blood eosinophilia in COPD. We studied the prospective relationship between eosinophilia at steady state and the subsequent number of COPD exacerbations. Methods: Data was taken from 13,780 general practice patients with a doctor diagnosis of COPD, blood eosinophil counts measured at steady state (> 4 weeks prior or after an exacerbation) and a 1 year subsequent follow-up, identified from the Optimum Patient Care Research Database. Rate Ratios (RR) were calculated using Quasi-Poisson regression. Results: Blood eosinophilia (≥ 0.5 x 10 9 /litre) was found in 10% of COPD patients, 37% of whom had ≥ 1 exacerbations. COPD patients with eosinophilia had a significantly higher rate of exacerbations than patients with normal values. The association was only significant in ex-smokers (53% of the population) and never-smokers (12%). No association was found in current smokers (35%) and in patients without maintenance treatments (28%). Within the subgroup of 4,785 COPD patients not currently smoking and using inhaled corticosteroids at baseline and follow-up year, patients with blood eosinophilia had a 24% higher exacerbation rate than patients without eosinophilia (RR=1.24 (1.10,1.41), adjusted for GOLD grade and host factors). Excluding patients with a record of asthma ever (42%) did not change this association. Conclusion: Blood eosinophilia occurs in stable (mostly treated) COPD patients and is associated with a higher exacerbation risk, especially in non-smokers receiving maintenance treatment. The inhibitory effect of current cigarette smoking on the relationship between blood eosinophilia and COPD exacerbations has to be further explored.