Relationship of blood eosinophil count to exacerbations in asthma patients with a COPD diagnosis

Abstract

Rationale: Elevated blood eosinophil count is a risk factor for future exacerbations in persistent adult asthma. We investigated whether a relationship also exists in asthma patients with a COPD diagnosis (AS-COPD). Methods: From pharmacy and healthcare utilization data in a Managed Care Organization, we identified 901 patients aged 18-64 years who met the HEDIS 2-year criteria for persistent asthma in 2009-2010, had ICD-9 diagnoses of COPD or chronic obstructive asthma (COA) during 2004-2010, and a blood eosinophil count in 2010. We examined the relationship between blood eosinophil count (2010) and asthma exacerbation rate in 2011 adjusting for demographics, disease burden, and comorbidities. Results: 65% of the AS-COPD cohort had at least one COPD, 69% one COA (2004-2010) and 79% one non-COA asthma diagnosis (2009-2010). A blood eosinophil cutoff point ≥400/mm 3 (2010) related best to future asthma exacerbations (adjusted RR=1.44, 95% CI 1.09, 1.90). Other factors in 2010 that remained statistically significant in the multivariable models were COA diagnosis, history of asthma exacerbations, ≥7 short-acting beta-agonist canisters dispensed, female gender, and obesity. Conclusions: Elevated blood eosinophil count was a risk factor for future asthma exacerbations in AS-COPD as reported in persistent asthma with no COPD/COA diagnoses, suggesting a common inflammatory mechanism in both phenotypes.