Melena an overview ScienceDirect Topics 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, Decisions: A 20 year old male with dark stool Department of Emergency Medicine Saint John Arjun 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,