How important is rectal bleeding in the diagnosis of bowel cancer and polyps?

Overt bleeding from the anus is a common symptom of colorectal cancer but most frequently arises from a benign anal source. The aim of this study was to determine how successfully general practitioners and gastroenterologists could differentiate anal from colorectal sources of bleeding before full colonic investigation. 145 consecutive patients aged 40 years and over who had presented to a GP with rectal bleeding of less than 6 months' duration were referred to a specialist for total colonic investigation. The source of bleeding was diagnosed as colorectal cancer in 15 patients (7 stage A, 3 stage B) and polyps in 11. Of 63 patients in whom GPs predicted an anal source of bleeding only, 11 were ultimately found to be bleeding from a colonic or rectal source. The gastroenterologists (after rigid sigmoidoscopy) predicted an anal source of bleeding in 97, in 5 of whom the source was ultimately found to be colorectal. All patients aged over 40 who present with recent rectal bleeding should be referred for full colonic investigation.