Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (159 page)

   In patients with iron deficiency, recommend upper and lower endoscopy plus workup for celiac disease

   Limitations

   Adenomas <2 cm in greatest diameter are less likely to bleed. Upper GI tract bleeding is less likely than lower GI tract bleeding to cause a positive test.

   Long-distance running is associated with positive guaiac test in ≤23% of runners.

   Stools may appear grossly normal with GI bleeding of 100 mL/day.

   Consistent melena requires 150–200 mL blood in the stomach.

GASTROINTESTINAL BLEEDING, SMALL INTESTINE

   The small intestine is an uncommon site of hemorrhage, accounting for only 3–5% of GI bleeding. Patients usually present with occult blood loss and may have evidence of melena or hematochezia.

   Differential Diagnosis of Gastrointestinal Bleeding from the Small Intestine (Table
5-4
)

   Angiodysplasia accounts for the majority of cases of bleeding from the small intestine (70–80%). Bleeding can be either brisk or occult. An isolated episode of bleeding does not mandate therapy, as the lesions do not usually rebleed (approximately 50%). Angiodysplasia may be an incidental finding and needs to be documented to be considered as a source of blood loss.

   Tumors account for 5–10% of cases of blood from the small intestine. Of these, one third are benign (leiomyoma and adenomas most commonly) and two thirds are malignant (45% adenocarcinoma, usually of the duodenum, 30% carcinoid, 14% lymphoma, and 11% leiomyosarcoma). The three most common malignancies are generally associated with chronic blood loss. Metastatic disease may also occur, most commonly from melanoma and breast cancer.

TABLE 5–4. Differential Diagnosis of Gastrointestinal Bleeding from the Small Intestine

   Laboratory Findings

   Plain abdominal films may show evidence of obstruction suggestive of stricture or tumor, but they are not likely to be diagnostic.