Association between Stress Hyperglycemia Ratio and Mortality in Critically Ill COPD Patients: A Mediation Analysis of White Blood Cell Count

Background: The stress hyperglycemia ratio (SHR), derived from admission glucose and HbA1c, reflects acute glycemic excursions. This study investigates the association between SHR and mortality in critically ill patients with chronic obstructive pulmonary disease (COPD), and explores the mediating role of white blood cell (WBC) count. Methods: A retrospective cohort analysis was conducted using the MIMIC-IV database (2008–2022). Adult ICU patients with COPD and available glucose and HbA1c data were included. SHR was categorized into tertiles (T1–T3). Primary and secondary outcomes were 28-day and 365-day all-cause mortality, respectively. Cox regression, restricted cubic spline (RCS) analysis, and Kaplan–Meier curves assessed associations. Mediation analysis evaluated the indirect effect of WBC count. Results: A total of 873 patients were included. Higher SHR (T3) was independently associated with increased 28-day (HR=1.35, 95% CI: 1.04–1.73, p=0.024) and 365-day mortality (HR=1.33, 95% CI: 1.11–1.59, p=0.002). RCS analysis revealed a linear relationship between SHR and mortality risk. Kaplan–Meier curves showed lower survival in the highest SHR group. WBC count partially mediated the effect of SHR on 28-day mortality (ACME, p<0.01), accounting for 4.45% of the total effect. Conclusions: SHR is an independent predictor of short- and long-term mortality in critically ill COPD patients. The association may be partially mediated by inflammation, as reflected by WBC count. SHR could serve as a simple tool for early risk stratification in this population. Clinical trial number: not applicable.