In this Article

• What is rectal bleeding?
• Definition and description of rectal bleeding
• Origin of rectal bleeding
• Occult gastrointestinal bleeding
• What are the causes of rectal bleeding?
• Anal fissure
• Hemorrhoids
• Diverticulosis
• Colon cancer and polyps
• Polypectomy
• Angiodysplasias
• Colitis and proctitis
• Meckel's diverticulum
• Rare causes of rectal bleeding
• How is the cause and site of rectal bleeding determined?
• History and physical examination
• Anoscopy
• Flexible sigmoidoscopy
• Colonoscopy
• Radionuclide scans
• Visceral angiogram
• Blood tests
• How is rectal bleeding treated?
• Correcting low blood volume and anemia
• Determining the cause and site of bleeding
• Stopping bleeding and preventing rebleeding
• Rectal Bleeding At A Glance
• Rectal Bleeding Glossary
• Rectal Bleeding Index

Origin of rectal bleeding (where the blood comes from)

Most rectal bleeding comes from the colon, rectum, or anus. The colon is the part of the gastrointestinal tract through which food passes after it has been digested in the small intestine. The colon is primarily responsible for removing water from the undigested food and storing it until it is eliminated from the body as stool. The rectum is the last 15 cm of the colon. The anus (anal canal) is the opening through which stool passes when it is being eliminated from the body. Together, the colon, rectum, and anus form a long (several feet in length), muscular tube that also is known as the large intestine, large bowel, or the lower gastrointestinal tract. (The esophagus, stomach, duodenum, and small intestine are referred to as the upper gastrointestinal tract.)

The colon can be divided further into three regions; the right colon, the transverse colon, and the left colon. The right colon, also known as the ascending colon, is the part of the colon into which undigested food from the small intestine is first deposited. It is furthest from the rectum and anus. The transverse colon forms a bridge between the right and the left colon. The left colon is made up of the descending colon and the sigmoid colon. The sigmoid colon connects the descending colon to the rectum.

The color of the blood during rectal bleeding often depends on the location of the bleeding in the gastrointestinal tract. Generally, the closer the bleeding site is to the anus, the blood will be a brighter red. Thus, bleeding from the anus, rectum, and the sigmoid colon tend to be bright red, whereas bleeding from the transverse colon and the right colon tend to be dark red or maroon.

In some patients bleeding from the right colon can be black, “tarry” (sticky) and foul smelling. The black, smelly and tarry stool is called melena. Melena occurs when the blood is in the colon long enough for the bacteria in the colon to break it down into chemicals (hematin) that are black. Therefore, melena usually signifies bleeding is from the upper gastrointestinal tract (for example: bleeding from ulcers in the stomach or the duodenum or from the small intestine) because the blood usually is in the gastrointestinal tract for a longer period of time before it exits the body. Sometimes melena may occur with bleeding from the right colon. On the other hand, blood from the sigmoid colon and the rectum usually does not stay in the colon long enough for the bacteria to turn it black.

Rarely, massive bleeding from the right colon, from the small intestine, or from ulcers of the stomach or duodenal can cause rapid transit of the blood through the gastrointestinal tract and result in bright red rectal bleeding. In these situations, the blood is moving through the colon so rapidly that there is not enough time for the bacteria to turn the blood black. Sometimes, bleeding from the gastrointestinal tract (upper or lower) can be too slow to cause either rectal bleeding or melena. For example, slow bleeding from colon polyps or cancers can cause small amounts of blood to mix and be lost within the stool. Special tests (fecal occult blood tests) are needed to demonstrate the blood.

Occult gastrointestinal bleeding

Rectal bleeding is a type of gastrointestinal bleeding. Rectal bleeding needs to be distinguished from another type of gastrointestinal bleeding, occult gastrointestinal bleeding. Occult gastrointestinal bleeding refers to a slow loss of blood into the upper or lower gastrointestinal tract that does not cause changes in the color of the stool or result in visible bright red blood. The blood is found only by testing the stool for blood (fecal occult blood testing) in the laboratory. Occult bleeding has many of the same causes as rectal bleeding and may result in the same symptoms as rectal bleeding. It is often associated with anemia that is due to loss of iron along with the blood (iron deficiency anemia). For more information, please see the colon cancer screening and fecal occult blood test articles.

Rectal Bleeding - How Was Diagnosis Established

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From the Doctors at MedicineNet.com

Colonoscopy - Learn about the colonscopy procedure, what it is, why it is performed, preparation, complications, alternatives and the after effects of the screening exam on MedicineNet.com Source:MedicineNet Fecal Occult Blood Test - Read about the fecal occult blood test in which there are two types, chemical and immunologic. Fecal occult blood tests are used to screen for colon cancer and colon polyps. Source:MedicineNet Flexible Sigmoidoscopy - Read about flexible sigmoidoscopy procedure used to examine the lower portion of the colon and rectum. It may be used to investigate the cause of rectal bleeding, bowel changes, rectal pain, and diarrhea. Source:MedicineNet Read 43 more Rectal Bleeding related articles ... FDA OKs New Crohn's Disease Drug Cimzia