Association between blood eosinophil count and in-hospital mortality among systemic corticosteroids-treated patients with COPD-bronchiectasis overlap: a retrospective cohort study.

Background: Systemic corticosteroids (SCS) are commonly used for acute exacerbation of COPD (AECOPD), but their effect in patients with COPD-bronchiectasis overlap remains unclear. Whether admission blood eosinophil count (BEC) modifies clinical outcomes in this population is not well-defined. Methods: This single-center retrospective cohort study included hospitalized AECOPD patients with radiologically confirmed bronchiectasis (2011-2020). Patients were stratified based on admission BEC. The independent associations of BEC with in-hospital mortality and other outcomes in SCS-treated COPD-bronchiectasis overlap patients were rigorously assessed using multivariable logistic regression and propensity score matching analyses. Results: Among 9,699 AECOPD patients, 1,421 (14.65%) had bronchiectasis. SCS use was more common in patients with greater disease severity and lower baseline BEC. In the overall overlap cohort, SCS was not independently associated with mortality after adjustment. However, BEC significantly modified this relationship. In patients with BEC <300 cells/μL, SCS use was associated with increased in-hospital mortality (adjusted OR 2.05, Conclusion: In this study, BEC appeared to modify the association between SCS and clinical outcomes in hospitalized COPD-bronchiectasis overlap patients. Observationally, SCS was associated with increased mortality in patients with low BEC, especially among the elderly and those with severe bronchiectasis, whereas no such risk was observed in patients with high BEC. These findings are hypothesis-generating and highlight the potential of BEC to inform personalized treatment strategies. However, they require rigorous prospective validation in randomized controlled trials before any clinical implementation can be considered.