Blood in the Stool (Rectal Bleeding)

  • Medical Author:
    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

  • Medical Editor: Bhupinder S. Anand, MBBS, MD, DPHIL (OXON)
    Bhupinder S. Anand, MBBS, MD, DPHIL (OXON)

    Bhupinder S. Anand, MBBS, MD, DPHIL (OXON)

    Dr. Anand received MBBS degree from Medical College Amritsar, University of Punjab. He completed his Internal Medicine residency at the Postgraduate Institute of medical Education and Research, Chandigarh, India. He was trained in the field of Gastroenterology and obtained the DPhil degree. Dr. Anand is board-certified in Internal Medicine and Gastroenterology.

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Flexible sigmoidoscopy

Flexible sigmoidoscopy utilizes a flexible sigmoidoscope, a fiberoptic viewing tube with a light at its tip. It is a shorter version of a colonoscope. It is inserted through the anus and is used by the doctor to examine the rectum, sigmoid colon and part or all of the descending colon. It is useful for detecting diverticula, colon polyps, and cancers located in the rectum, sigmoid colon, and descending colon. Flexible sigmoidoscopy also can be used to diagnose ulcerative colitis, ulcerative proctitis, and sometimes Crohn's colitis and ischemic colitis.

Despite its value, flexible sigmoidoscopy cannot detect cancers, polyps, or angiodysplasias in the transverse and right colon. Flexible sigmoidoscopy also cannot diagnose colitis that is beyond the reach of the flexible sigmoidoscope. Because of these limitations, colonoscopy may be necessary. The advantage of flexible sigmoidoscopy over colonoscopy is that it can be accomplished with no preparation of the colon or after only one or two enemas.


Colonoscopy is a procedure that enables an examiner (usually a gastroenterologist) to evaluate the inside of the entire colon. This is accomplished by inserting a flexible viewing tube (the colonoscope) into the anus and then advancing it slowly under direct vision through the rectum and the entire colon. The colonoscope frequently can reach the part of the small intestine that is adjacent to the right colon.

Colonoscopy is the most widely used procedure for evaluating rectal bleeding as well as occult bleeding. It can be used to detect polyps, cancers, diverticulosis, ulcerative colitis, ulcerative proctitis, Crohn's colitis, ischemic colitis, and angiodysplasias throughout the entire colon and rectum.

If there is any possibility that the bleeding is coming from a location above the colon, and esophagogasatroduodenal endoscopic examination (EGD) also should be done to identify or exclude an upper gastrointestinal source of bleeding.

Radionuclide scans

There are two types of radionuclide scans that are used for determining the site of gastrointestinal bleeding; a Meckel's scan, and a tagged red blood cell (RBC) scan.

The Meckel's scan is a scan for detecting a Meckel's diverticulum. A radioactive chemical is injected into the patient's vein, and a nuclear camera (like a Geiger counter) is used to scan the patient's abdomen. The radioactive chemical will be picked up and concentrated by the acid-secreting tissue in the Meckel's diverticulum and will appear as a "hot" area in the right lower abdomen on the scan.

Tagged RBC scans are used to determine the location of the gastrointestinal bleeding. After drawing blood from the bleeding patient, a radioactive chemical is attached to the patient's red blood cells and the "tagged" red blood cells are injected back into the patient's vein. If there is active gastrointestinal bleeding, the radioactive red blood cells leak into the intestine where the bleeding is occurring and will appear as a hot area with a nuclear camera. One drawback of the tagged RBC scan is that bleeding will not show as a hot area if there is no active bleeding at the time of the scan. Thus, it can fail to diagnose the site of bleeding if bleeding is intermittent and the scan is done between bleeding episodes. Another drawback of the scan is that it requires a reasonable amount of bleeding to form a hot area. Thus, it can fail to diagnose the site of the bleeding if bleeding is too slow. The tagged RBC scan is safe, and can be done quickly and without discomfort to the patient.

Unfortunately, the tagged RBC scans are not very accurate in defining the exact location of the bleeding; there is often a poor correlation between where the tagged RBC scan shows the bleeding to be and the actual site of bleeding found at the time of surgery. Therefore, tagged RBC scans cannot be relied upon to help surgeons decide what area of the gastrointestinal tract to remove in the event the bleeding is severe or persistent and requires surgery. However, if the scan shows a hot area, it usually means there is active bleeding, and the patient may be a candidate for a visceral angiogram to more accurately locate the site of bleeding.

Visceral angiogram

A visceral angiogram is an X-ray study of the blood vessels of the gastrointestinal tract. The doctor (usually a specially trained radiologist) will insert a thin, long catheter into a blood vessel in the groin and, under X-ray guidance, will advance the tip of the catheter into one of the mesenteric arteries (arteries that supply blood to the gastrointestinal tract). A radio-opaque dye is injected through the catheter and into the mesenteric artery. If there is active bleeding, the dye can be seen leaking into the gastrointestinal tract on the X-ray film. Visceral angiograms are accurate in locating rapid bleeding in the gastrointestinal tract, but it is not useful if the bleeding is slow or has stopped at the time of the angiogram.

The visceral angiogram is not widely used because of its potential complications such as kidney damage from the dye, allergic reactions to the dye, and the formation of blood clots in the mesenteric arteries. It is reserved for patients who have severe and continuous bleeding and in whom colonoscopy cannot locate the site of the bleeding.

Medically Reviewed by a Doctor on 5/4/2016

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