Association between the preoperative serum albumin-to-creatinine ratio (sACR) and in-hospital mortality in perioperative patients with chronic kidney disease: a cohort study based on INSPIRE database.

Objective: The serum albumin-to-creatinine ratio (sACR) is a potential biomarker for multiple diseases, yet its prognostic role in chronic kidney disease (CKD) patients undergoing surgery remains unexplored. This study aimed to investigate the association between sACR levels and postoperative in-hospital mortality in this population. Methods: This retrospective cohort study analyzed 2,611 CKD patients from the INSPIRE database (2011-2020). Patients were stratified into tertiles based on admission sACR levels. Multivariable Cox regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between sACR and mortality. Restricted cubic spline (RCS) analysis was performed to assess potential nonlinear relationships. Sensitivity analyses were conducted to verify result robustness. Results: The cohort had a mean age of 61.1 ± 14.8 years and a median sACR of 1.2 (interquartile range: 0.7-2.6). Multivariable analysis revealed that each unit increase in sACR was associated with a 29% reduction in mortality (adjusted HR 0.71, 95% CI 0.61-0.83, p < 0.001). Compared with the lowest tertile (T1), the highest tertile (T3) demonstrated a 48% lower mortality risk (HR 0.52, 95% CI 0.33-0.82, p = 0.005). RCS analysis identified a nonlinear, L-shaped association between sACR and mortality (P for nonlinearity < 0.001), with a threshold effect observed at approximately 2.7. Sensitivity analyses confirmed the robustness of these findings. Conclusion: Lower sACR levels are independently associated with higher in-hospital mortality in surgical CKD patients, exhibiting an L-shaped relationship with a critical threshold at 2.7. sACR represents a practical, cost-effective early-warning biomarker for perioperative risk stratification in this high-risk population.