What does melena indicate when observed in stool?

Melena refers to the passage of black, tarry stools, which signifies the presence of digested blood in the gastrointestinal tract. This black coloration occurs due to the prolonged exposure of blood to digestive enzymes and bacteria as it moves through the intestines. Typically, melena suggests bleeding from a source in the upper gastrointestinal tract, such as from a bleeding ulcer or gastritis. The tarry nature of the stool is a key characteristic that helps distinguish melena from other types of gastrointestinal bleeding, such as hematochezia, which involves bright red blood typically indicative of bleeding from the lower gastrointestinal tract. Understanding these distinctions is vital for accurate diagnosis and treatment in a clinical setting.