Blood Urea Nitrogen-to-Creatinine Ratio to Differentiate Upper From Lower Gastrointestinal Bleeding: A Systematic...

Determining the location of gastrointestinal (GI) bleeding is critical for guiding diagnostic and therapeutic strategies but often results in patients receiving pan-endoscopy with upper endoscopy, colonoscopy, and small bowel capsule endoscopy, which can be unnecessary, costly, and waste limited healthcare resources. The blood urea nitrogen-to-creatinine ratio (BUN/Cr) may help discriminate between upper GI bleeding (UGIB) and lower GI bleeding (LGIB). This study aims to assess the diagnostic performance of the BUN/Cr in distinguishing UGIB from LGIB.

A literature search was conducted in MEDLINE, EMBASE, and Cochrane Library to identify diagnostic test accuracy studies published from inception through January 31, 2025, which evaluated BUN/Cr in patients with UGIB versus LGIB. A linear mixed-effects model meta-analysis was conducted using the "diagmeta" package. The pooled sensitivity, specificity, diagnostic odds ratio, and area under the summary receiver operating characteristic curve (AUC) were estimated, and optimal threshold was determined using the Youden index.

Seventeen studies were included in this meta-analysis. The pooled mean difference in BUN/Cr between UGIB and LGIB patients was 11.44 (95% confidence interval [95% CI] 8.35-14.52). At a threshold of > 30, pooled sensitivity was 38.8% (95% CI 28.1%-50.8%) and specificity was 89.3% (95% CI 81.0%-94.2%). At the optimal cut-off of 22, sensitivity was 66.2% (95% CI 57.8%-73.7%), specificity was 71.0% (95% CI 58.5%-81.0%), and AUC was 0.740 (95% CI 0.683-0.794).

BUN/Cr demonstrates moderate diagnostic accuracy for distinguishing UGIB from LGIB, particularly at a threshold of ≥ 22. This readily accessible and inexpensive blood test may assist in early clinical triage and assessment of the location of GI bleeding, particularly in those patients where the clinical presentation is obscure.