Capsule endoscopy is the most appropriate diagnostic test for this patient with obscure gastrointestinal bleeding. Obscure gastrointestinal bleeding refers to recurrent or persistent bleeding from the gastrointestinal tract without an obvious source on endoscopic studies. The evaluation of gastrointestinal bleeding of obscure origin usually begins with repeat endoscopy directed at the most likely site. Approximately 30% to 50% of lesions can be detected using this approach. If repeat endoscopy is unrevealing in a patient who is not actively bleeding, examination should focus on the small intestine, using such tests as capsule endoscopy. Wireless capsule endoscopy allows excellent visualization of the small bowel. Unlike angiography and technetium scans, wireless capsule endoscopy is effective even in the absence of active bleeding. Wireless capsule endoscopy detects the source of occult bleeding in 50% to 75% of patients. In patients with iron deficiency anemia, in whom bleeding can be episodic, capsule endoscopy is another way to investigate potential sources of blood loss after other investigations have been unrevealing. This patient, who is on anticoagulation and has heme-positive stool, is likely to have vascular lesions such as angiodysplasia in the small bowel. Angiodysplasia is the most common cause of small-bowel bleeding in older patients.

Angiography and technetium-labeled nuclear scans are used in patients with active bleeding (melena or hematochezia) who are transfusion dependent and hospitalized. This patient does not meet these criteria.

Intraoperative endoscopy is generally employed only as a last resort for the evaluation of obscure gastrointestinal bleeding. The patient undergoes laparotomy or laparoscopy, and the bowel is evaluated with a colonoscope following surgical enterotomy. This technique should only be used if other less invasive options have been exhausted or if a patient has unexplained, life-threatening bleeding. In addition, the yield is somewhat low (approximately 25%).