Objective  To explore the diagnostic performance of blood urea nitrogen-to-creatinine (BUN/Cr) ratio in differentiating the site of gastrointestinal bleeding, and to assess the predictive value of early elevated BUN/Cr ratio for clinical outcomes in patients with acute nonvariceal upper gastrointestinal bleeding (ANVUGIB).

  Methods  The adult patients diagnosed with gastrointestinal bleeding who were hospitalized in the Department of Gastroenterology, Zhongshan Hospital, Xiamen University between May 2020 and May 2021 were retrospectively enrolled. According to the site of gastrointestinal bleeding, the patients were divided into the upper gastrointestinal tract group, the proximal small intestinal bleeding group, and the distal small intestinal and colonic bleeding group. According to the early dynamic changes of BUN/Cr ratio within 6-48 hours after admission, patients with ANVUGIB were divided into early dynamic elevated BUN/Cr ratio group and non-early dynamic elevated BUN/Cr ratio group. Receiver operating characteristic (ROC) curve was used to analyze the diagnostic performance of BUN/Cr ratio in differentiating the site of gastrointestinal bleeding and examine the predictive efficacy of early dynamic elevated BUN/Cr ratio after admission, Rockall scoring system, and the combined indicator of the two for estimating the primary clinical outcomes in ANVUGIB patients.

  Results  A total of 266 patients were enrolled. Among them, 204 cases were in the upper gastrointestinal bleeding group, 15 cases were in the proximal small intestinal bleeding group, and 47 cases were in the distal small intestinal and colonic bleeding group. In the ANVUGIB patients, 16 were in the group with early dynamic elevated BUN/Cr ratio after admission, and 146 were in the group with non-early dynamic elevated BUN/Cr ratio after admission. The area under the ROC curve of the BUN/Cr ratio was 0.831 (95% CI: 0.780-0.874), the optimal cut-off value being 34.59 mg/g for differentiation between upper and lower gastrointestinal bleeding. The area under the ROC curve of the BUN/Cr ratio was 0.901 (95% CI: 0.798-0.963) and the optimal cut-off value was 19.27 mg/g for differentiation between proximal small intestinal bleeding and the distal small intestinal and colonic bleeding. The area under the ROC curve of the early dynamic elevated BUN/Cr ratio after admission was 0.806 (95% CI: 0.737-0.864) for predicting the primary clinical outcome in patients with ANVUGIB. The area under the ROC curve of the combined indicator included the early dynamic elevated BUN/Cr ratio after admission and the Rockall scoring system was 0.909 (95% CI: 0.854-0.949) for predicting the primary clinical outcome in patients with ANVUGIB.

  Conclusion  The BUN/Cr ratio shows rather reliable diagnostic performance for identifying the site of gastrointestinal bleeding, and the early dynamic elevated BUN/Cr ratio after admission is a reliable indicator for predicting clinical outcomes in patients with ANVUGIB.