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causes of upper gastrointestinal bleeding. Other frequent causes of upper GI bleeding include esophageal varices, trauma to the lower esophagus (Mallory-Weiss tear) and neoplasia. In most cases a specific cause will be determined. Therapeutic endoscopy has resulted in a significant reduction in the likelihood of rebleeding, and the need for transfusion, surgery and prolonged hospitalization.

The timing of colonoscopy for suspected lower GI bleeding is less urgent as most causes of lower GI bleeding will cease spontaneously. Common causes of lower GI bleeding include angiodysplasia (particularly from the right side of the colon), diverticular disease, carcinoma, inflammation and, in children, Meckel's diverticulum of the small bowel. The success of determining the cause is enhanced when adequate bowel preparation has taken place.

Despite careful endoscopic examination, the cause of bleeding will not be determined in a small percentage of cases. It is in this select group of patients that nuclear medicine scanning is most useful. The overall accuracy may be as low as 45%, however, as bleeding is intermittent. This scenario occurs more commonly in the setting

Figure 5. An approach to the investigation of lower GI bleeding.

of suspected lower GI bleeding. Nuclear medicine scanning can detect smaller rates of bleeding than angiography, is less invasive and may help to focus the efforts of the angiographer. As angiography offers the potential of therapeutic intervention, the decision as to whether a GI bleeding scan is performed in conjunction with angiography or not is dictated by the urgency of the clinical situation (Fig. 5).

Clinical Role of Urea breath testing

The discovery of the causal relationship between the gram-negative spiral rod, Helicobacter pylori, and peptic ulcer disease (PUD) has dramatically changed the investigation and approach to therapy. While only a small number of patients that harbor H. pylori develop PUD, most patients with PUD are infected with H. pylori. Although the diagnosis of H. pylori infection can be established by histological examination of gastric biopsy specimens, urea breath testing is non-invasive, inexpensive and highly accurate (over 95% sensitivity and specificity).

Technical Considerations

Urea breath testing relies upon the fact that the urease enzyme is not present in mammalian cells and H. pylori is the only bacteria commonly found in the stomach that contains the enzyme. Following an overnight fast the patient swallows a small amount of 14C-urea. Gastric H. pylori cleaves the urea into ammonium and 14C-bicarbonate which is absorbed into the bloodstream (Fig. 6). Under the action of carbonic anhydrase, bicarbonate is transformed into 14C-carbon dioxide, which is exhaled in the breath. Carbon-14 activity in the breath is therefore an indicator of H. pylori urease activity.

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