What is the cause of recurrent melena stool with multiple telangiectasia and prominent veins in the proximal ascending colon in a 14 year old boy? What Does Clay Colored Stool Mean Understanding Melena: What Does It Mean When You Have Dark Stools? Fortis Healthcare Melena vs hematochezia symptoms and differences 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, Dark Stool Causes: Understanding Color Changes