Blood eosinophil count as a biomarker for therapy guidance in COPD and asthma exacerbations

This Journal club evaluates recent evidence on the role of blood eosinophil count (BEC) as a biomarker to guide therapy in patients with acute exacerbations of COPD and asthma. The review focuses on three studies with different methodological approaches: a biomarker-directed corticosteroid trial (Bafadhel et al., 2012), an acute biologic therapy trial using benralizumab (ABRA, 2025) and a long-term biologic therapy trial using mepolizumab (COPD-HELP, 2025). The biomarker-directed corticosteroid study demonstrated non-inferior symptom improvement while reducing steroid exposure, highlighting the potential to personalise therapy based on BEC. The ABRA trial showed that a single injection of benralizumab reduced treatment failure, prolonged time to exacerbation and improved symptom scores in patients with high eosinophils. By contrast, the COPD-HELP trial found no significant effect of mepolizumab on readmission or mortality, despite substantial eosinophil reduction. Limitations include small sample sizes, heterogeneous populations and reliance on surrogate end-points in some studies. These findings support the use of BEC-guided therapy in acute settings but suggest that long-term biologic treatment post-exacerbation may not improve hard outcomes. Future research should focus on precision medicine strategies targeting eosinophilic exacerbations and identifying patient subgroups who benefit most from biomarker-guided interventions.