Differential Diagnosis for Dark Tarry Stool

• Single most likely diagnosis
  • Gastrointestinal bleeding (upper GI bleed): This is the most likely diagnosis because dark tarry stools, also known as melena, are a classic sign of upper gastrointestinal bleeding. The black color and tarry consistency are due to the digestion of blood by intestinal enzymes.
• Other Likely diagnoses
  • Iron supplements: Taking iron supplements can cause dark stools due to the oxidation of iron.
  • Certain foods (e.g., licorice, blueberries, blackberries): Some foods can temporarily cause dark-colored stools due to their pigmentation.
  • Bismuth subsalicylate (e.g., Pepto-Bismol): This medication can cause black stools due to the bismuth component.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Upper GI malignancy: Although less common, upper gastrointestinal cancers (e.g., stomach or esophageal cancer) can cause bleeding leading to melena.
  • Esophageal varices: Bleeding from esophageal varices, often due to liver cirrhosis, can present with melena and is a medical emergency.
  • Aortic-enteric fistula: A rare but potentially life-threatening condition where there is a fistula between the aorta and the intestine, leading to gastrointestinal bleeding.
• Rare diagnoses
  • Hemobilia: Bleeding from the biliary tree into the gastrointestinal tract, which can cause melena.
  • Hematochezia with rapid transit: Although less common, if blood from a lower GI source moves quickly through the intestines, it may not be fully digested and could present as melena instead of the typical bright red blood.