Summary
Objective: to determine the percentage of patients with severe asthma and exacerbations and evaluated the costs of the disease based on blood eosinophil counts.Methods: A retrospective observational study based on the review of medical records in Spain was carried out. Patients ≥18 years of age requiring care during the years 2014-2015; diagnosed with asthma with at least 2 years of continuous records (at least one year prior to the index date defined as the first asthma medication prescription and at least one year after the index date) were included. Study groups: eosinophil counts <300 cells/μl and ≥300 cells/μl. Main variables: comorbidity, clinical parameters, exacerbations and annual asthma total costs.Results: A total of 268 severe asthmatic patients in Spain were included, representing 6.3% of the asthma population, with 58.6% having eosinophil count ≥300 cells/μl and 41.4% eosinophil count <300 cells/μl. The mean age was 56.1 years (63.4% women). Patients with eosinophilic inflammation (≥300 cells/μl) had lower FEV1 values (54.3% vs. 60.7%; p < .001), poorer treatment adherence (65.6% vs. 77.3%; p < .001), and a greater mean number of exacerbations (3.3 vs. 1.9; p < .001). Exacerbations were correlated to FEV1 (β=‒.606), eosinophils (β = .255), immunoglobulin E (β = .152), and age (β = .128), p < .001. The mean total asthma annual cost (ANCOVA) was 6222 vs. 4152 euros, respectively (p = .016). Health costs were associated with age (β = .323), FEV1 (β = .239), eosinophils (β = .177) and exacerbations (β = .158), p < .01.Limitations: Those inherent to retrospective studies; the possible inaccuracy of diagnostic coding referring to severe asthma and other comorbidities and the external validity of the results.Conclusions: Health costs of patients with severe asthma were high. Total annual asthma costs and resource use were greater in patients with ≥300 cells/μl. Age, eosinophilia, exacerbations and FEV1 were associated with greater resource utilization and costs for the health system.

Relevance
Blood eosinophil counts were associated with exacerbations. The costs related to patients with severe asthma were high. Age, eosinophilia, exacerbations and the severity of asthma were associated with an increased use of healthcare resources and greater costs for the health system.