The presence of a GI bleed should be confirmed by inspecting the stool for melena or hematochezia and the NG tube aspirate for blood. The site of bleeding can frequently be determined from the patient’s complaints. Upper GI bleeding often presents with hematemesis combined with melena; hematochezia with a negative NG aspirate suggests a lower GI source.
Reference: Sleisenger MH, Fordtran JS (eds): Gastrointestinal Disease: Pathophysiology, Diagnosis, and Management, 7th ed. Philadelphia, W.B. Saunders, 2003.