Early postoperative rectal bleeding as a warning sign of anastomotic leak after colorectal surgery

Anastomotic leak remains one of the most severe complications following colorectal surgery. While multiple preoperative and intraoperative risk factors have been described, early postoperative clinical signs that may herald anastomotic failure have been scarcely investigated. The clinical significance of early postoperative rectal bleeding remains poorly defined. A retrospective observational study was conducted using a prospectively maintained database including adult patients who underwent colorectal surgery with primary anastomosis between January 2010 and May 2025. Early postoperative rectal bleeding was defined as visible blood loss per rectum within the first 48 postoperative h. Patients were divided into two groups according to the presence or absence of rectal bleeding. Demographic, operative, and postoperative variables were analyzed, and multivariate logistic regression was performed to identify independent predictors of anastomotic leak. A total of 1318 patients were included; 41 (3.1%) presented early postoperative rectal bleeding. Patients with rectal bleeding had a significantly higher incidence of anastomotic leak compared with those without bleeding (24.4% versus 6.3%, p = 0.001). In the multivariate analysis, early postoperative rectal bleeding was identified as an independent risk factor for anastomotic leak (OR 4.11; 95% CI 1.90–8.90; p = 0.001). Early postoperative rectal bleeding is an uncommon event but identifies a subgroup of patients at higher risk of anastomotic leak. Rather than being considered a benign complication, early postoperative rectal bleeding within the first 48 h should be regarded as an early warning sign that justifies increased clinical vigilance and a lower threshold for postoperative surveillance and diagnostic evaluation.