May 24, 2016
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Blood in the Stool (Rectal Bleeding) (cont.)

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How is the cause of blood in the stool (rectal bleeding) diagnosed?

An accurate diagnosis of the location and the cause of rectal bleeding is important for proper treatment, and prevention of further bleeding. Diagnosis relies on the history and physical examination, anoscopy, flexible sigmoidoscopy, colonoscopy, radionuclide scans, angiograms, and blood tests.

History and physical examination

The age of the patient may offer an important clue to the cause of rectal bleeding. For example, moderate to severe rectal bleeding in teenagers and young adults is more likely to come from a Meckel's diverticulum. Moderate or severe rectal bleeding in older individuals is more likely to be due to diverticulosis or angiodysplasias. Mild rectal bleeding in an adult with prior abdominal radiation treatment may be due to radiation proctitis.

The presence or absence of other symptoms also may provide important clues. Bleeding from diverticulosis, angiodysplasias, and Meckel's diverticula usually is not associated with abdominal or rectal pain. Rectal bleeding from ischemic colitis is often preceded by the sudden onset of lower abdominal, crampy pain. Fever, abdominal pain, and diarrhea often occur with colitis due to infection, ulcerative colitis, or Crohn's colitis. Mild bleeding accompanied with pain in the anal area during defecation (passing of stool) suggests bleeding from an anal fissure. A recent change in bowel habit such as increasing constipation or diarrhea suggests the possibility of cancer of the colon.

Inspection of the anus may disclose bleeding from a hemorrhoid or anal fissure. Unfortunately, most hemorrhoids and fissures are not actively bleeding at the time a patient arrives at the doctor's office. Thus, even if a doctor finds a hemorrhoid or anal fissure, he/she cannot be certain that they are the cause of the bleeding. Therefore, flexible sigmoidoscopy or colonoscopy will have to be done to exclude other potentially more serious causes of bleeding.


An anoscope is a three-inch long, tapering, metal or clear plastic, hollow tube approximately one inch in diameter at its wider end. The anoscope is lubricated, and the tapered end is inserted into the anus, through the anal canal, and into the rectum. As the anoscope is withdrawn, the area where internal hemorrhoids and anal fissures are found is well seen. Straining by the patient, as if they are having a bowel movement, may make hemorrhoids more prominent.

Whether or not hemorrhoids and anal fissures are found, if there has been rectal bleeding, the colon above the rectum needs to be examined to exclude other important causes of bleeding. Examination above the rectum can be accomplished by either flexible sigmoidoscopy or colonoscopy, procedures that allow the doctor to examine approximately one-third or the entire colon, respectively.

Medically Reviewed by a Doctor on 5/4/2016


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