Blood Eosinophil Count and Outcomes in Severe Uncontrolled Asthma: A Prospective Study

Background: Severe uncontrolled asthma (SUA) is associated with increased asthma exacerbations. Whether high blood eosinophil counts are related to this burden is uncertain.

Objectives: To determine the relationship of blood eosinophil counts to asthma exacerbations, utilization, and cost in patients with SUA.

Methods: Patients with persistent asthma (age ≥ 12 years) were identified administratively with SUA in phase I by evidencing (1) 2 or more asthma exacerbations; (2) 6 or more medium- or high-dose dispensed canisters of inhaled corticosteroid (ICS) as monotherapy or with long-acting β₂-agonist; and (3) 3 or more dispensed non-ICS controllers. Of the 541 patients with SUA invited to participate in the prospective phase II follow-up study, 261 (48.2%) had blood tests (index date) to determine eosinophil count and other atopic biomarkers. The relationship of blood eosinophil cutoff points to asthma exacerbations and direct costs 1 year after the index date were determined by multivariable regression.

Results: A blood eosinophil cutoff point of greater than or equal to 400 cells/mm³ compared with less than 400 cells/mm³, but not 150 cells/mm³ or 300 cells/mm³, was a risk factor in the outcome year in adjusted analyses for 2 or more asthma exacerbations (risk ratio, 1.55; 95% CI, 1.02-2.35; P =.04) and any asthma emergency department visit or hospitalization (risk ratio, 2.29; 95% CI, 1.16-4.55; P =.02), but not for rate of asthma exacerbations or incremental total direct asthma costs per patient ($202; 95% CI, -286 to 691).

Conclusions: A high blood eosinophil count was an independent risk factor for 2 or more asthma exacerbations or any asthma emergency department visit or hospitalization, but not direct costs in patients with SUA, possibly constrained by limited power.