Prognostic Value of Red Blood Cell Distribution Width for Mortality in Critically Ill Patients with Acute Pancreatitis

Background Acute pancreatitis (AP) is a common gastrointestinal emergency with unpredictable progression and high mortality in severe cases. Traditional prognostic scores such as APACHE II, BISAP, and SOFA are limited by complexity and delayed applicability. Red blood cell distribution width (RDW), a simple and universally available biomarker, has emerged as a potential prognostic indicator. This study assessed the predictive value of RDW for short- and long-term mortality in critically ill patients with AP. Methods We conducted a retrospective cohort study using the MIMIC-IV database. Adult patients with a primary diagnosis of AP were included, with exclusions for repeat admissions, ICU stay < 48 h, hematologic malignancy, or end-stage renal disease. Baseline RDW at ICU admission was the primary exposure. Primary outcomes were 28-day and 90-day all-cause mortality. Associations were evaluated using Kaplan–Meier analysis, Cox regression, restricted cubic splines, and subgroup analyses. Incremental prognostic performance was assessed with AUC, net reclassification index (NRI), and decision curve analysis (DCA). Results A total of 450 patients met inclusion criteria. The overall 28-day and 90-day mortality rates were 8.7% and 12.0%, respectively. Patients with elevated RDW (> 14.5%) had significantly higher mortality at both 28 days (13.4% vs. 4.3%, p  < 0.001) and 90 days (18.7% vs. 6.5%, p  < 0.001). In fully adjusted Cox models, RDW remained an independent predictor of mortality (28-day: HR = 1.31, 95% CI: 1.15–1.50; 90-day: HR = 1.28, 95% CI: 1.16–1.41). RDW demonstrated strong discriminatory ability (AUC: 0.837 for 28-day, 0.807 for 90-day mortality). Incorporating RDW into baseline models improved predictive accuracy (ΔAUC + 0.06; NRI = 0.21, p  < 0.001), and DCA showed greater net clinical benefit. Conclusion RDW is a low-cost, widely accessible biomarker that independently predicts short- and long-term mortality in critically ill patients with AP. Its inclusion in conventional prognostic models enhances risk stratification and may support earlier, tailored clinical decision-making. Prospective multicenter validation is warranted.