The GI tract runs from mouth to anus and can be divided into an upper and a lower portion. The upper segment runs from the mouth to the first part of the small intestine, and the lower extends from there to the end of the GI tract. Lower GI bleeds are caused by inflammation, anatomic lesions, vascular disease, infections or mass lesions, says Access Medicine.
Inflammatory Bowel Disease
According to FamilyDoctor.org, inflammatory bowel disease includes Crohn's disease and ulcerative colitis. The ultimate factors that cause these diseases remain unknown, but it is thought to involve the immune system. Crohn's disease occurs anywhere along the GI tract, forming patches of ulcers and inflammation that may extend through the thickness of the bowel wall. Typical symptoms include diarrhea and abdominal pain. People with Crohn's may also develop gallstones and kidney stones. In contrast, ulcerative colitis is confined to the colon and does not extend through the bowel wall. It may affect the entire colon, however, and is more likely to present with bleeding.
Anatomic Lesions
The most common anatomic lesion leading to lower GI bleeding is diverticulosis. This is a sac like out-pouching of the intestinal wall. It often occurs at sites where arteries run through the intestinal wall, exposing the blood vessel to the inside of the intestine, and increasing the chances of a lower GI bleed. Risk factors include a low fiber high fat diet according to the National Digestive Diseases Information Clearinghouse.
Vascular Disease
Vascular disease responsible for lower GI bleeds include angiodysplasia and ischemia. Angiodysplasia is a disorganized arrangement of blood vessels that is more common with age and has a tendency to cause lower GI bleeds. Ischemic colitis occurs from a blocked blood vessel. According to the UpToDate website, the term "ischemia" refers to a lack of blood. Ischemic bowel causes sudden, cramping pain, an urge to defecate and passage of bloody stool.
Infection
Food poisoning may also cause lower GI bleeds. Bacterial organisms such as Shigella, Campylobacter, and Salmonella are common causes, UptoDate. An infectious cause of lower GI bleeding is more likely to present with fevers than the others. Important clues from the history that point to infections as the cause of lower GI bleeding include the presence of a fever and multiple people developing similar symptoms. Improperly cooked food is generally the source of these infections.
Mass Lesion
Mass lesions such as cancers or polyps may present with bleeding as well. Cancerous tissue may invade blood vessels in the wall of the intestine. Colon cancers often occur without symptoms, emphasizing the need for screening by a health care practitioner. A major risk factor is age. Other risk factors include a history of colon cancer or colon cancers in the family, or a history of ulcerative colitis. Diet may or may not play a role, reports UpToDate.
Other Sources
Other sources of lower GI bleeding include hemorrhoids and anal fissures, which may cause bright red bleeding. The ingestion of some foods and drugs may also falsely appear to cause a GI bleed. Foods include red grapes and beets. Activated charcoal and bismuth containing medicines such as Pepto-Bismol may also look like a GI bleed. False positives on tests for lower GI bleeds may occur when patients take Vitamin C supplements or consume red meat, horseradish or turnips, reports EB Medicine.
References
- Access Medicine; Lower gastrointestinal (GI) bleeding
- Family Doctor.org; Inflammatory Bowel Disease
- National Digestive Diseases Information Clearinghouse; Diverticulosis and Diverticulitis
- UpToDate: Etiology of Lower Gastrointestinal Bleeding in Adults
- EB Medicine: Gastrointestinal Bleeding: An evidence based ED approach to risk stratification.
