What Causes Bleeding From the Rectum?

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Some of the most common causes of rectal bleeding are hemorrhoids, chronic constipation, anal fissures and passing hard stools, states Mayo Clinic. Rectal bleeding is also a symptom of anal cancer, colon polyps, ulcerative colitis, inflammation of the rectum and Crohn's disease.

Several problems with the colon, anus and rectum can cause rectal bleeding, reports Mayo Clinic. A condition called angiodysplasia causes rectal bleeding because there are abnormal blood vessels near the intestines. Diverticulosis, severe diarrhea, sores on the rectal walls and rectal prolapse can also cause rectal bleeding.

Minor rectal bleeding refers to the presence of small amounts of bright red blood in the stool, in the toilet or on a piece of toilet paper used to wipe the anus after a bowel movement, explains the American Society for Gastrointestinal Endoscopy. This type of rectal bleeding should be evaluated if it does not go away within 24 to 48 hours, recommends Mayo Clinic.

Emergency medical assistance is needed for a person with rectal bleeding who displays signs of shock. These include quick, shallow breathing; dizziness when rising to a standing position; fainting; nausea; and confusion. Cold, clammy skin and reduced urine output are other possible signs of shock.

During an evaluation for rectal bleeding, a doctor examines the anus for signs of hemorrhoids, anal fissures and other problems, states the American Society for Gastrointestinal Endoscopy. If necessary, the doctor performs a digital rectal examination to look for problems with the anus and lower rectum. In some cases, it may be necessary to have a colonoscopy or flexible sigmoidoscopy to determine the cause of rectal bleeding.