Chapter 31. Acute Lower Gastrointestinal Bleeding

• Diverticulosis, arteriovenous malformations, and ischemic colitis are the most common causes of lower GI bleeding.
• Clinical presentation ranges from occult to overt bleeding.
• Endoscopic and radiologic tests can provide both diagnosis and therapy.
• Urgent colonoscopy may have increased diagnostic yield but does not clearly lead to decreased rates of rebleeding.

Lower gastrointestinal (GI) bleeding is defined as bleeding that occurs from a source distal to the ligament of Treitz. This chapter discusses only colonic sources of bleeding; upper GI bleeding and obscure (small bowel) GI bleeding are explored elsewhere (see Chapters 30 and 33).

Lower GI bleeding accounts for about 20% of major GI bleeding and is less common and generally less severe than upper GI bleeding. There are 20–27 hospitalizations per 100,000 adults in the United States due to lower GI bleeding. It generally occurs in older adults with a mean age between 63 and 77 years old. Nearly 80% of lower GI bleeding stops spontaneously, similar to upper GI bleeding. The overall mortality rate of lower GI bleeding is 2–4%. Similar to upper GI bleeding, patients who begin lower GI bleeding as outpatients have a significantly lower mortality rate (3.6%) than those who develop lower GI bleeding as inpatients (23%).

Definition of Bleeding

Hematochezia is defined as bright red blood per rectum and usually implies a left colonic source, although it can be caused by a more brisk, proximal source of bleeding. Maroon stools are maroon-colored blood mixed with stool and are often associated with a right colonic source of bleeding; however, they also can result from a more brisk, proximal source of bleeding. Melena refers to black, tarry, foul-smelling stool that results from the bacterial degradation of hemoglobin over a period of at least 14 hours. It usually implies an upper GI source of bleeding although it may be associated with right colonic bleeding in cases of slow motility. Ingestion of iron, bismuth, charcoal, and licorice should be excluded since they all can turn stool black. Occult blood refers to the presence of 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. Blood loss of at least 5–10 mL/day can be detected by stool guaiac card tests. The GI tract normally loses about 0.5–1.5 mL of blood per day, which is not usually detected by guaiac tests.

Diagnostic Approach

When patients initially present with lower GI bleeding, they should be triaged and managed based on the severity of the hemorrhage (Figure 31–1).