Black Stool Differential Diagnosis

The differential diagnosis for black stool can be organized into the following categories:

• Single Most Likely Diagnosis
  • Peptic ulcer disease (PUD) with upper GI bleeding: This is the most common cause of black stool, also known as melena. The black color is due to the digestion of blood in the stomach and small intestine.
• Other Likely Diagnoses
  • Gastritis: Inflammation of the stomach lining can cause bleeding, leading to black stool.
  • Esophageal varices: Enlarged veins in the esophagus can bleed, causing black stool.
  • Mallory-Weiss tear: A tear in the mucous membrane of the lower end of the esophagus can cause bleeding.
  • Gastrointestinal malignancy: Tumors in the stomach or small intestine can cause bleeding, leading to black stool.
• Do Not Miss Diagnoses
  • Aortic enteric fistula: A fistula between the aorta and the intestine can cause massive bleeding, leading to black stool. This is a life-threatening condition that requires prompt diagnosis and treatment.
  • Dieulafoy's lesion: A rare cause of upper GI bleeding, characterized by a small, superficial ulceration in the stomach wall.
  • Hemobilia: Bleeding from the biliary tree can cause black stool, and may be a sign of a serious underlying condition such as a liver tumor or gallstones.
• Rare Diagnoses
  • Black licorice ingestion: Eating large amounts of black licorice can cause black stool due to the presence of a compound called licorice root.
  • Iron supplementation: Taking iron supplements can cause black stool due to the oxidation of iron in the gut.
  • Bismuth subsalicylate ingestion: Taking medications containing bismuth subsalicylate, such as Pepto-Bismol, can cause black stool due to the bismuth component.
  • Intussusception: A rare condition in which a part of the intestine telescopes into another part, causing bleeding and potentially leading to black stool.