Melena

Causes

Peptic ulcer disease is the most common cause, but any bleeding in the upper gastrointestinal tract or ascending colon can produce melena. Anticoagulant medications such as warfarin may also lead to melena. Other causes include malignant tumors of the esophagus, stomach, or small intestine; hemorrhagic blood diseases like thrombocytopenia and hemophilia; gastritis; stomach cancer; esophageal varices; Meckel's diverticulum; and Mallory-Weiss syndrome. False melena can result from iron supplements, bismuth subsalicylate, Maalox, lead, swallowed blood from epistaxis, or dietary blood such as black pudding or the Maasai diet. A self-limiting case may occur in newborns two to three days after delivery from swallowed maternal blood.

Diagnosis

In acute cases with substantial blood loss, patients may present with anemia or low blood pressure, though many have few symptoms aside from the melena itself. Upper endoscopy is often the first approach to identify an obvious bleed; when the source is unclear, an upper endoscopy is recommended to locate it. Lower gastrointestinal bleeding typically presents with hematochezia or frank blood. A tagged red blood cell scan, though limited in sensitivity and specificity, may detect slow bleeding at a rate of 0.5 ml/min; mesenteric angiogram with or without embolization is the gold standard, while colonoscopy is often first line.

Bleeding from the lower tract, such as the sigmoid colon or rectum, usually produces bright red blood, especially if brisk; melena occurs only when blood originates more proximally or when lower bleeding is slow enough for enzymatic breakdown. Roughly 14 hours of transit time is needed for blood breakdown in the intestinal lumen; shorter transit yields hematochezia, longer yields melena. A common rule that melena only arises from sources above the ligament of Treitz is unreliable due to frequent exceptions.