Prognostic Value of the Serum Creatinine-to-Albumin Ratio for Short-term and Long-term Mortality Among Patients with Aortic Aneurysm: A Retrospective Cohort Study Running title: Creatinine-to-albumin ratio predicts mortality in patients with aortic aneurysms

Background Aortic aneurysm is a life-threatening vascular disorder marked by progressive aortic dilation. Early stages are often clinically silent, and diagnosis depends predominantly on incidental imaging, which limits opportunities for timely treatment. Conventional inflammatory and thrombotic biomarkers demonstrate modest specificity and are vulnerable to systemic confounders. The serum creatinine-to-albumin ratio-a composite indicator of inflammation, metabolic stress, and nutritional status-has proven prognostic relevance in other cardiovascular settings but remains unexamined in aortic aneurysm. Methods We conducted a retrospective cohort study using adult patient data from the MIMIC-III and MIMIC-IV intensive care databases. Baseline serum creatinine and albumin measurements defined the ratio, and an optimal cutoff (0.391) was derived by maximally selected rank statistic. Patients were stratified into high- and low-ratio groups. Kaplan-Meier analysis compared 28-day and one-year survival probabilities, while multivariable Cox proportional hazards models quantified the ratio’s association with mortality, adjusting for demographic and clinical covariates. Restricted cubic spline regression assessed nonlinear risk relationships, and sensitivity analyses at 90 and 180 days verified temporal consistency. Subgroup analyses evaluated effect modification by age, aneurysm rupture, and other key factors. Results Among 1,970 patients, a CAR of ≥ 0.391 was associated with significantly worse survival. Multivariate Cox regression revealed higher CAR levels were linked to increased mortality risk: 28-day mortality (hazard ratio (HR) 1.53; 95% confidence interval (95%CI) 1.09–2.14) and 1-year mortality (HR 1.51; 95% CI 1.24–1.85). Kaplan-Meier analysis showed reduced survival rates in high CAR patients at all time points ( P  < 0.001). Sensitivity analyses confirmed consistent associations with 90-day and 180-day mortality ( P  < 0.001). Restricted cubic spline analysis demonstrated a nonlinear increase in mortality risk with rising CAR values. Subgroup analyses identified older patients and those with ruptured aneurysms as particularly vulnerable. Conclusion The serum creatinine-to-albumin ratio is a simple, low-cost prognostic biomarker in aortic aneurysm. A cutoff of 0.391 reliably identifies individuals at elevated short-term and long-term mortality risk, supporting its use in early risk stratification and personalized management.