What is Melena
Melena is the passage of black tarry stools, representing digested blood in the gastrointestinal tract. 1
Clinical Definition and Characteristics
Melena specifically refers to black, tarry stools with a sticky consistency and characteristic odor, distinguishing it from simple black stools that may result from dietary factors or medications. 2 The black color results from blood that has been exposed to gastric acid and digestive enzymes, causing hemoglobin to be converted to hematin. 1
Key Distinguishing Features
Black stools lacking the sticky, tar-like consistency and characteristic odor typically do not represent melena and generally do not require urgent gastrointestinal evaluation unless other concerning features are present. 2
Melena differs from other forms of gastrointestinal bleeding presentation:
Anatomic Source and Clinical Significance
Melena typically indicates bleeding proximal to the ligament of Treitz (upper gastrointestinal tract), though it can occasionally result from slow bleeding in the right colon. 2, 3 The presence of melena doubles the odds of finding a bleeding source within the proximal small intestine among patients with obscure gastrointestinal bleeding. 3
Common Causes
The most frequent causes of melena include: 1
- Peptic ulcer disease (35-50% of cases)
- Gastroduodenal erosions (8-15%)
- Esophagitis (5-15%)
- Esophageal varices (5-10%)
- Mallory-Weiss tears (15%)
- Vascular malformations (1%)
- Upper gastrointestinal malignancy
In children, the upper gastrointestinal tract is the most common bleeding source, with duodenal ulcer being the most frequent diagnosis. 4
Clinical Severity Assessment
Patients presenting with both hematemesis and melena generally have more severe bleeding than those presenting with melena alone. 1 The severity of bleeding can be categorized as:
- Massive bleeding: Often associated with esophageal varices (66.7% of massive bleeds) 5
- Moderate bleeding: 25% of presentations 5
- Mild bleeding: 67.5% of presentations 5
Mortality Implications
The presence of melena in the context of upper gastrointestinal bleeding carries significant mortality risk: 1
- 11% mortality in patients admitted to hospital for bleeding
- 33% mortality in those who develop bleeding while hospitalized for other reasons
- Elderly patients with significant comorbidities have the highest mortality rates
Clinical Pitfalls
Massive upper GI bleeding can present as bright red blood per rectum (hematochezia) rather than melena if transit time is rapid enough, which can mislead clinicians about the bleeding source. 2 Always obtain a detailed medication and dietary history to identify non-bleeding causes when evaluating black stools, as iron supplements, bismuth, and certain foods can mimic melena's appearance. 2