Single most likely diagnosis
- Gastrointestinal bleeding (upper GI bleed): 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, which turns it into a dark, tar-like substance.
Other Likely diagnoses
- Iron supplements: Taking iron supplements can cause black stools due to the oxidation of iron.
- Bismuth subsalicylate (Pepto-Bismol): This medication can also cause black stools due to the bismuth component.
- Foods: Certain foods like licorice, blueberries, and blackberries can temporarily cause black stools.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Upper GI malignancy: Although less common, black stools can be a sign of a gastrointestinal malignancy, such as stomach or esophageal cancer.
- Variceal bleeding: Bleeding from esophageal varices can cause black stools and is a life-threatening condition.
- Aortic-enteric fistula: A rare but potentially fatal condition where there is a connection between the aorta and the intestine, causing bleeding.
Rare diagnoses
- Hemobilia: Bleeding from the biliary tree into the gastrointestinal tract, which can cause black stools.
- Hematochezia from a distal source: Although less common, black stools can occasionally be caused by bleeding from a distal source, such as the colon or rectum, especially if the bleeding is slow and the blood has time to be digested.