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Key Clinical Questions

  • image What risk factors increase the severity of lower gastrointestinal (GI) bleeding?

  • image What are the indications for tagged red blood cell scan and angiography in the setting of lower GI bleeding?

  • image What are the indications for surgery in patients with diverticular bleeding and ischemic colitis?

  • image What medical treatment options are available to treat recurrent lower GI bleeding from angiodysplasias?

  • image What is the pathophysiology of ischemic colitis?

Lower gastrointestinal (GI) bleeding refers to bleeding that occurs from a source in the colon, rectum, or anus. There are about 36 hospitalizations per 100,000 adults in the United States due to lower GI bleeding. Lower GI bleeding accounts for about 20% of major gastrointestinal bleeding and is less common and generally less severe than upper GI bleeding. It affects the older population with a mean age between 63 and 77 years old, and incidence of lower GI bleeding is increasing in the elderly especially over age 80. Nearly 80% of all GI bleeding, including lower GI bleeding, stops spontaneously. The overall mortality rate of lower GI bleeding is 1.5%. Patients who begin lower GI bleeding as an outpatient have a significantly lower mortality rate (3.6%) than in patients who develop lower GI bleeding (23%), which is similar to upper GI bleeding.


Definitions of bleeding

Hematochezia refers to bright red blood per rectum and often implies a left colonic source, although it can be caused by a more brisk, proximal source of bleeding. Maroon stools are stools mixed with maroon-colored blood that are usually associated with a right colonic source of bleeding; however, they can also result from a more brisk, proximal source of bleeding. Melena is black, tarry, foul smelling stool that results from bacterial degradation of hemoglobin over at least 14 hours. It implies an upper GI source of bleeding, although it may occur from a right colonic bleeding source. Occult blood refers to small quantities of blood in the stool that does not change its color and can only be detected by performing a stool guaiac card test. The gastrointestinal tract normally loses about 0.5 to 1.5 mL of blood per day, which is not detected by guaiac tests. A threshold blood loss of at least 5 to 10 mL/d is necessary before detection by stool guaiac card tests.


  • Ingestion of iron, bismuth, charcoal, and licorice should be excluded as they all can turn stool black.


History in these patients should focus on factors associated with potential etiologies (Table 161-1). A differential diagnosis should be developed based on presenting complaints and physical examination. Patients should be asked about symptoms that might indicate hemodynamic compromise including dyspnea, chest pain, light-headedness, and fatigue.

TABLE 161-1History Features Based on Bleeding Etiology

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