Hematochezia vs melena: Comparing symptoms, causes, and treatment When is stool color concerning? GASTROINTESTINAL HEMORRHAGE (2): Melena. Melena, the passage of black, tarry stools, usually implies blood loss greater than 500 ml originating anywhere between the oropharynx and the right hemicolon. Melena occurs most often, Different stool colours can provide important clinical clues related to digestion, bleeding, liver disease, malabsorption, infection, or bowel inflammation. Disclaimer For educational purposes only. Not medical advice. Consult a qualified Melena an overview ScienceDirect Topics Melena: What Is It, Causes, Symptoms, Bleeding, Treatment, and More Osmosis