What are the diagnostic steps for melena?

Diagnostic Approach to Melena

The diagnosis of melena requires visual confirmation of black, tarry stools followed by a systematic evaluation to identify the bleeding source, with upper endoscopy being the first-line diagnostic test as most cases originate from the upper GI tract. 1, 2

Definition and Initial Assessment

Melena refers to black, tarry stools resulting from the digestion of blood in the gastrointestinal tract. Key diagnostic steps include:

• Visual confirmation: True melena appears as black, sticky, tarry stools with a characteristic offensive odor
• Digital rectal examination: Essential to confirm the presence of melena and rule out other causes of dark stools
• Hemodynamic assessment: Evaluate for signs of shock, tachycardia, hypotension, or orthostatic changes 3
• Laboratory tests: Complete blood count, coagulation profile, and blood chemistry to assess severity and guide management

Diagnostic Algorithm

1. Confirm melena is present

   • Black, tarry stools (not just dark brown)
   • Positive fecal occult blood test

2. Assess severity of bleeding

   • Hemodynamic parameters (heart rate, blood pressure)
   • Hemoglobin level (Hb ≤8.0 g/dL suggests massive bleeding) 3
   • Need for blood transfusion (>1000 mL within one hour or >2000 mL within 24 hours indicates massive bleeding) 3

3. Determine likely source

   • Melena typically indicates bleeding proximal to the ligament of Treitz (upper GI tract) 4
   • The presence of melena doubles the odds of finding a bleeding site within the proximal small intestine 4

4. Diagnostic testing sequence:

   • Upper endoscopy (EGD): First-line diagnostic test for melena
   • Colonoscopy: If EGD is negative (diagnostic yield is approximately 4.8% after negative EGD) 5
   • Small bowel evaluation: If both EGD and colonoscopy are negative
     • Capsule endoscopy
     • Deep enteroscopy (antegrade approach preferred with melena) 4

Special Considerations

• Timing of endoscopy: Urgent endoscopy (within 24 hours) for active bleeding or hemodynamic instability
• Preparation for endoscopy: Gastric lavage may be necessary to improve visualization during urgent upper endoscopy
• Therapeutic potential: Endoscopy serves both diagnostic and therapeutic purposes 1

Common Pitfalls to Avoid

• Misidentifying dark stools: Not all dark stools are melena (medications, foods, and bismuth can cause dark stools)
• Incomplete evaluation: Failure to evaluate the small bowel after negative upper and lower endoscopies
• Delayed diagnosis: Postponing endoscopy in patients with significant bleeding
• Overlooking occult sources: Assuming upper GI source without appropriate testing

Melena strongly suggests upper GI or proximal small intestinal bleeding, but approximately 5% of cases may originate from the colon, particularly the right side 5. Therefore, a thorough evaluation is necessary when the initial EGD is negative.