Lower GI bleeding usually presents as hematochezia, or passage of maroon or bright red blood or blood clots per rectum. This is different from upper Gi bleeding, which usually presents with hematemesis and/or melena. Although helpful, these distinctions are not absolute. in up to 11% of patients with hematochezia, the culprit lesion is identified in the upper GI tract. Conversely, 19% of patients with lower GI bleeding can present with melena. Overall, the acuity and severity of lower Gi bleeding is less than upper Gi bleeding. According to a survey of members of the American College of Gastroenterology (ACG), patients with lower GI bleeding were less likely to present to the physician with shock or orthostasis compared with patients with upper GI bleeding (19% versus 35%, respectively) and less likely to require blood transfusions (36% versus 64%, respectively). Lower GI bleeding is self-limiting in approximately 80% of cases, although intermittent bleeding episodes do occur. The incidence of lower GI bleeding, as well as its morbidity and mortality, increases with age due to the higher rate of comor-bid conditions and use of medications. The reported mortality rate varies between 2.0 to 3.6%.
The causes of lower GI hemorrhage vary depending on the age of the patient and the severity of the bleeding. In patients under the age of 50 years, the most common causes are infectious colitis, anorectal disease, and inflammatory bowel disease (IBD). In older patients, significant hematochezia is usually due to diverticulosis, angiodyspla-sia, neoplasia,or ischemia (Table 101-1).
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