Non-linear Relationship between Uric Acid to Albumin Ratio and Mortality in Pediatric Intensive Care Unit Patients: A Large-Scale Observational Study

Purpose The prognostic value of the uric acid to albumin ratio (UAR) in critically ill children is unknown. We aimed to investigate the association between admission UAR and mortality in the pediatric intensive care unit (PICU) and to characterize the nature of this relationship. Patients and methods: This retrospective cohort study enrolled 6,686 critically ill children from the Pediatric Intensive Care (PIC) database. The primary outcome was 28-day ICU mortality. The relationship between UAR and mortality was explored using multivariable logistic regression. Restricted cubic splines (RCS) and a two-piecewise linear regression model were performed to assess for non-linearity and threshold effects. Kaplan-Meier analysis, receiver operating characteristic (ROC) curves, and mediation analysis were also conducted. Results In the fully adjusted model, UAR was independently associated with an increased risk of 28-day ICU mortality (OR = 1.25, 95% CI: 1.13–1.37, P  < 0.001). Patients in the highest UAR quartile (Q4) had a significantly higher mortality risk compared to the lowest quartile (Q1) (OR = 1.94, 95% CI: 1.34–2.82, P  < 0.001). Kaplan-Meier analysis confirmed a significantly lower survival probability in the Q4 group ( P  < 0.001). RCS analysis revealed a non-linear relationship ( P for non-linearity < 0.05), identifying a significant inflection point at UAR = 2.815. Below this threshold, the mortality risk increased more steeply (OR = 1.95, 95% CI: 1.49–2.53). The predictive ability of UAR for 28-day ICU mortality (AUC = 0.700) was superior to its individual components. Lactate was found to partially mediate the association, accounting for 35.18% of the total effect. Conclusion Our study identifies admission UAR as a novel, independent predictor of mortality in a large cohort of critically ill children. As a simple and universally available biomarker, UAR holds significant promise for improving early risk stratification in the PICU.