The passage of blood from the anus or rectum. The blood can vary in colour from dark brown to black to bright red. It can be mixed with, or on the surface of, faeces or passed separately. Rectal bleeding can or cannot be accompanied with pain.
Haemorrhoids (swollen veins in the lining of the anus) are the most widespread cause of rectal bleeding. Little amounts of bright red blood appear on the surface of toilet paper or faeces. Anal fissure (a tear at the margin of the anus), anal fistula (an abnormal anal channel), procititis (inflammation of the rectum), or rectal prolapse (protrusion of the rectal lining) can also bring on bleeding from the rectum.
Cancer of the rectum or colon or polyps (grape-like growths) can also create bleeding. Disorders of the colon, such as diverticular disease, can give dark red faeces. Black faeces can be due to bleeding from high in the digestive tract. Bloody diarrhoea can be caused from ulcerative colitis, shigellosis, or amoebiasis.
Diagnosis can be made from a proctoscopy, rectal examination, sigmoidoscopy, or colonoscopy (internal examination using a flexible or rigid viewing instrument), or double-contrast barium X-ray examination. Rectal bleeding in any person over the age of 40 should be cautiously investigated to draw out the possibility of colorectal cancer.