Diagnostic accuracy of the blood urea-to-creatinine ratio for differentiating AKI etiologies and dialysis prediction in adults: A systematic review and meta-analysis.

BACKGROUND: The blood Urea-to-Creatinine Ratio (UCR) is one of the most readily available markers for differentiating the etiology of acute kidney injury and has long been emphasized in textbooks and review articles. Nevertheless, its diagnostic accuracy has not yet been systematically evaluated. METHODS: We searched PubMed, Embase, and the Cochrane Library through May 2025. The diagnostic performance of the UCR for (1) Pre-renal azotemia/transient AKI and (2) Non-dialysis-requiring AKI was extracted and evaluated. A diagnostic accuracy meta-analysis was conducted using a bivariate model. We also compared the diagnostic accuracy of fractional excretion of sodium with UCR to predict pre-renal azotemia/transient AKI. RESULTS: We identified 9 studies comprising 10 independent cohorts with a total of 16,412 participants. For pre-renal azotemia/transient AKI, the UCR demonstrated a pooled sensitivity of 0.74 (95% CI 0.43-0.91) and specificity of 0.52 (95% CI 0.21-0.82), with an AUC of 0.69. For non-dialysis-requiring AKI, the UCR showed a pooled sensitivity of 0.49 (95% CI 0.44-0.55) and specificity of 0.71 (95% CI 0.64-0.77), with an AUC of 0.63. Substantial heterogeneity was observed, and the certainty of evidence was rated low to very low. CONCLUSIONS: Based on currently available evidence, despite its long-standing role in textbooks and review articles, UCR demonstrates limited diagnostic accuracy for differentiating AKI etiologies and identifying non-dialysis-requiring AKI. Its clinical utility should be interpreted with caution given the substantial heterogeneity and low certainty of evidence, and it may be more appropriate to use UCR in combination with, or in place of, other traditional indices or novel biomarkers.