Can melena (black, tarry stools) occur in lower gastrointestinal (GI) bleeding?

Can Melena Occur in Lower GI Bleeding?

Yes, melena can occur in lower gastrointestinal bleeding, though it is less common than hematochezia (bright red blood per rectum). 1

Clinical Presentation of Lower GI Bleeding

Lower GI bleeding typically presents with hematochezia, but melena can occur as a manifestation of lower GI sources:

• Patients with acute lower GI hemorrhage may present with bright red blood per rectum, dark blood with clots, or less commonly, melena. 1
• The ACR Appropriateness Criteria explicitly recognizes that lower GI tract bleeding can manifest clinically as either hematochezia or melena in hemodynamically stable patients. 1

When to Suspect Lower GI Sources in Melena

While melena classically suggests upper GI bleeding (proximal to the ligament of Treitz), lower GI sources should be considered in specific contexts:

• After a nondiagnostic upper endoscopy (EGD), colonoscopy identifies a suspected bleeding source in 4.8% of patients presenting with melena. 2
• Patients with melena and negative EGD are at increased risk for colorectal tumors (OR 2.87) compared to screening populations. 2
• Small bowel sources (technically lower GI) account for 0.7-9.0% of cases presenting with severe hematochezia, and these can present with melena. 1

Critical Diagnostic Pitfall to Avoid

Approximately 10-15% of patients presenting with acute severe hematochezia actually have an upper GI source identified on upper endoscopy. 1

• This means the converse is also true: some patients with melena will have lower GI sources.
• Always perform upper endoscopy first in patients with melena to exclude the more common upper GI sources before proceeding to colonoscopy. 1
• If upper endoscopy is nondiagnostic and melena persists, colonoscopy should be performed as these patients have increased risk of colorectal pathology. 2

Practical Management Algorithm

For patients presenting with melena:

1. Perform upper endoscopy first - this remains the highest yield initial test. 1
2. If EGD is nondiagnostic and bleeding continues, proceed to colonoscopy - diagnostic yield is 4.8% for identifying bleeding sources. 2
3. Consider small bowel evaluation if both upper and lower endoscopy are negative, as small bowel sources (angiodysplasia, tumors, NSAID ulcers) can present with melena. 3
4. In obscure GI bleeding with melena, the presence of melena doubles the odds (OR 1.97) of finding a bleeding site in the proximal small intestine, suggesting antegrade deep enteroscopy as the preferred approach. 4

Clinical Context

The therapeutic intervention rate during colonoscopy for melena after nondiagnostic EGD is only 1.7%, but the procedure remains justified given the increased cancer risk in this population. 2