A retrospective cohort study in severe asthma describing commonly measured biomarkers: Eosinophil count and IgE levels.

Abstract

Identifying asthma patients suitable for biologic therapy includes the assessment of blood biomarkers (IgE and eosinophils (EOS)). How they relate to each other is unclear. This retrospective, database study used routinely collected clinical data to identify and evaluate an asthma cohort (classification code for asthma; ≥ 18 years; ≥1 prescription for asthma; ≥1 estimation of serum IgE, in 2 years prior to index date). Distribution into high and low IgE and EOS groups (IgE cut-point: > or ≤75 kU/L; EOS cut point: >or ≤400 μ/L), and characteristics by group are described. In patients with severe asthma (British Thoracic Society Step (BTS) ≥4; N=884), using maximum recorded IgE/EOS, 33% had high IgE/high EOS, 28% low IgE/low EOS and approximately a fifth each had high IgE/low EOS or low IgE/high EOS. Proportions were similar when EOS values measured 2 or 4 weeks before an exacerbation were excluded. Using EOS/IgE 'same day' measurements (N=578) only identified half of the high EOS group. Patients in high IgE groups were more likely to be younger males without comorbid COPD; those in high EOS groups were more likely to be on BTS treatment Step 5 vs 4. The low IgE/low EOS group had the lowest incidence of asthma-related hospital attendances, the highest incidence was observed in the high EOS groups. Maximum available EOS measurement irrespective of exacerbations may be relevant when considering therapy. These data showed low IgE/Low EOS to be more benign and high EOS groups at increased risk of frequent, severe exacerbations.