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Dark Blood in Stool – Causes of Melena

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Melena is the term used to describe black tarry feces which is a result of “old” and degraded blood in the stool. It usually indicates an upper gastrointestinal bleed originating within the esophagus, stomach or duodenum of the small intestine. Less frequently, bleeding from the mouth or nose may also be responsible but this is more clearly evident when vomiting (hematemesis), coughing (hemoptysis) and in the nasal discharge (epistaxis) or sputum (saliva, phlegm). If there is slow transit time (GI motility), the bleed could be from lower down the gut which typically presents with fresh blood in the stool (hematochezia).

As little as 50 ml of blood in the upper gut can result in melena although it usually requires 100 to 200ml before it becomes clearly evident. While it is reported that melena results in foul-smelling stool, this is sometimes difficult to differentiate from the normal odor. The smell of “old” blood emanating from the stool may accompany the black tarry appearance of the feces.

If there are any signs of shock, the condition needs to be treated as a medical emergency.

Causes of Dark Blood in the Stool

These conditions may arise secondary to the contributing factors listed below.

  • Esophagitis
  • Esophageal cancer
  • Gastritis
  • Bleeding stomach ulcer (refer to Causes of Stomach Bleeding)
  • Duodenitis
  • Bleeding duodenal ulcer
  • Varices of the esophagus or stomach
  • Mallory-Weiss tear
  • Tumors of the gastrointestinal tract
  • Arteriovenous malformation
  • Meckel’s diverticulum

Contributing Factors

  • Gastroesophageal reflux disease (GERD)
  • Liver cirrhosis
  • Certain drugs that are known to cause an upper GI bleed like aspirin and other NSAID’s
  • Trauma to the gastrointestinal tract, which includes investigative medical procedures like an upper GI endoscopy and surgery
  • Foreign body lodged in the gut or passing through the gut
  • Gut infections like H.pylori (stomach) or the various causes of infectious gastroenteritis (stomach and duodenum). Esophageal infections due to candida or herpes may be seen in immunocompromised patients like in HIV/AIDS
  • Generalized infections like typhoid fever and yellow fever. Rare infections include the Ebola virus and icteric leptospirosis (Weil disease)
  • Venom from poisonous insects, arachnids, reptiles
  • Metals like in arsenic poisoning
  • Pest and rodent poisons
  • Drug (ingested) overdose
  • Alcohol poisoning
  • Thrombocytopenia
  • Bleeding disorders like hemophilia

Related Articles

  1. What is Melena?
  2. Black Bowel Movement and Black Diarrhea

Article reviewed by Dr. Greg. Last updated on September 2, 2010