Classic "outlet" rectal bleeding does not require full colonoscopy to exclude significant pathology

Full diagnostic colonoscopy often is performed to exclude significant pathology in patients presenting with rectal bleeding. In patients with classic "outlet" bleeding, defined as bright red blood after or during defecation, with no family history of colorectal neoplasia or change in bowel habits, we hypothesize that the diagnostic yield of complete colonoscopy will be low. The purpose of this study was to determine whether complete colonoscopy is necessary in the evaluation of patients with "outlet" rectal bleeding.

Information for all patients undergoing colonoscopy by a single endoscopist was prospectively recorded. Before each colonoscopy, a complete history, including indication for the examination, was obtained. Using standard definitions, patients with outlet bleeding, suspicious bleeding, hemorrhage, and occult bleeding were accessed and the findings of their colonoscopies were analyzed. Institutional permission was obtained.

A total of 9,098 patients had colonoscopy recorded in the database, and 703 had the indication of outlet bleeding, 251 suspicious bleeding, 204 occult bleeding, and 67 hemorrhage. Of the patients with outlet bleeding, only 47 (6.7 percent) had significant lesions on colonoscopy (adenomas >1 cm, villous adenomas, cancer in situ, or invasive cancer). By contrast a greater number of significant lesions were present in patients with all other types of bleeding (17.2 percent; P<0.001). The incidence of invasive cancer was significantly lower in the outlet bleeding group compared with other types of bleeding (1 vs. 3.6 percent; P<0.01). Patients with outlet bleeding were much less likely than patients with other bleeding to have isolated right-sided colonic pathology. Younger patients with outlet bleeding have a particularly low yield on colonoscopy. In 182 patients younger than aged 50 years with outlet bleeding, only 3 (1.6 percent) had adenomas >1 cm and no invasive cancers were detected.

In patients with classic outlet bleeding, the yield of a complete diagnostic colonoscopy is low. If the history is classic for outlet bleeding and no other indication for colonoscopy exists, flexible sigmoidoscopy is enough to exclude significant pathology.