Association of Anion Gap to Bicarbonate Ratio (ABR) with 28-Day Mortality in ICU Sepsis: A Retrospective Cohort Study Based on the MIMIC-IV Database

Background Sepsis-associated mortality remains a critical challenge in intensive care units, with metabolic dysregulation being a hallmark of its pathophysiology. While the anion gap-to-bicarbonate ratio (ABR) has been proposed as a potential biomarker for acid-base homeostasis, its prognostic utility in sepsis patients is yet to be comprehensively validated. This study investigates the correlation between ABR and 28-day mortality in ICU sepsis patients. Methods Based on the MIMIC-IV database, patients with sepsis who were admitted to the ICU for the first time (n = 22,549) were included. The relationship between ABR and 28-day mortality was evaluated using the Cox proportional hazards model and adjusted for multiple factors. Subgroup analysis was conducted using Kaplan-Meier curves and forest plots. Results The 28-day mortality rate of patients in the high ABR group (ABR > 0.6786) was significantly higher than that of the low ABR group (HR = 2.33, 95% CI: 2.26–2.41, p < 0.001). After multivariate adjustment, ABR remained significantly associated with mortality (HR = 1.40, 95% CI: 1.27–1.55, p < 0.001). Subgroup analysis showed that the impact of ABR on mortality was particularly significant in patients with cerebrovascular disease, diabetes, and metastatic solid tumors (P for interaction < 0.05). Conclusion ABR is an independent predictor of 28-day mortality in ICU patients with sepsis, especially with significant prognostic value in specific subgroups.