Bleeding from the lower intestinal tract may be categorized as profuse or massive, mild, and occult. With profuse bleeding, there is usually a sudden passage of bright red or maroon-colored blood from the rectum, often associated with weakness and faintness. Many times the patients have had few or no previous symptoms, and abdominal symptoms and signs at the time of hemorrhage are minimal. Massive bleeding in young adults is most often due to ulcerative colitis. When this condition is excluded, diverticulosis and, less often, arteriovenous malformations are most frequently responsible for massive colonic bleeding. When massive bleeding is caused by diverticular disease, the bleeding lesion is usually in the ascending colon; the ascending colon and cecum are also the main sites of arteriovenous malformations that bleed. Cancer and polyps seldom cause acute massive bleeding.
Mild, usually intermittent bleeding from the rectum is all too often attributed to the hemorrhoids by both patients and physicians when the bleeding in fact is due to another cause. Pain in the anal area associated with the passage of bright red blood alone suggests bleeding from a fissure, thrombosed hemorrhoid, carcinoma that has infiltrated the sphincter, or rectal disease. Streaks of red blood on the stool, blood passed with mucus, diarrhea, tenesmus, or urgency will suggest rectal or sigmoid colon disease. Blood originating from the ascending colon is dark red unless the rate of bleeding is rapid. It also is characteristically mixed in with the stool rather than clinging to the surface of formed stool, as typically occurs when bleeding originates in the descending colon.
Occult bleeding may arise from any site in the gastrointestinal tract. Diseases that can cause hematemesis, melena, black stools, or the passage of red or dark red blood may also cause occult bleeding. It may be difficult to tell without laboratory testing whether dark or black stools or vomited or regurgitated material contains blood. It may be difficult to detect occult blood loss even though bleeding is sufficient to cause anemia, particularly when bleeding is intermittent. Problems related to occult bleeding may present in different ways. Some patients have symptoms, e.g., gastrointestinal or those due to anemia, while others have only unexplained iron deficiency anemia. In some, occult blood is found in the feces during routine or screening examinations. A positive occult blood test, however, is not necessarily indicative of disease; it may result from trauma caused by a cleansing or barium enema or by proctosigmoidoscopy. When a positive test is found in a single stool sample, the clinical setting will help to determine whether investigation should be undertaken promptly or deferred. For example, if occult bleeding is demonstrated in a patient who has been taking aspirin but who has no gastrointestinal symptoms, further investigation need not be undertaken unless the stools continue to show occult blood about 10 days after the aspirin has been discontinued.