High Blood Eosinophil Count Is a Risk Factor for Future Asthma Exacerbations in Adult Persistent Asthma

BACKGROUND: Exacerbation-associated uncontrolled asthma represents a major public health problem. The relationship of elevated blood eosinophils to this process needs study. OBJECTIVE: To determine whether a high blood eosinophil count is a risk factor for future asthma exacerbations in adult persistent asthma. METHODS: By using electronic pharmacy and health care data from Kaiser Permanente Southern California, 2392 patients, ages 18 to 64 years, were identified who met the Health Effectiveness Data and Information Set 2-year criteria for persistent asthma, did not manifest chronic obstructive pulmonary disease and other major illnesses, and had a blood eosinophil determination in 2010. Exacerbations (primary outcome) were defined as asthma outpatient visits that required systemic corticosteroid dispensing within +/-7 days or asthma emergency department visits or hospitalizations. A period of >= 8 days defined a new exacerbation. Multivariate modelling used negative binomial and Poisson regression to examine the association between a blood eosinophil count determined in 2010 and risk of exacerbations, and >= 7 short-acting beta(2)-agonist (SABA) canisters dispensed (secondary outcome) in 2011 by adjusting for demographics, comorbidities, and asthma burden. RESULTS: The rate of asthma exacerbations in 2011 was 0.41 events per person year (95% CI, 0.37-0.45). Eosinophil count >= 400/mm(3) in 2010 was a risk factor for asthma exacerbations in 2011 (adjusted rate ratio 1.31 [95% CI, 1.07-1.60]; P = .009) and >= 7 SABA dispensed (adjusted risk ratio 1.17 [95% CI, 1.03-1.1.33]; P = .015). CONCLUSION: A high blood eosinophil count is a risk factor for increased future asthma exacerbations and excessive short-acting beta(2)-agonist use after adjustment of potential confounders in adults with persistent asthma, which suggests a higher disease burden in patients with asthma and with high blood eosinophil counts. (C) 2014 American Academy of Allergy, Asthma & Immunology