Melena, Causes, Signs and Symptoms, Diagnosis and Treatment YouTube Stool Colour Chart A quick clinical guide to interpret stool color changes and their possible causes. Stool appearance can give important clues about gastrointestinal healthbut always correlate with history, examination, and Melena: What Is It, Causes, Symptoms, Bleeding, Treatment, and More Osmosis 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,