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

Background: 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. Methods: 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 mu/L), and characteristics by group are described. Findings: 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. Conclusion: 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.