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Melena is a form of blood in stool which refers to the dark black, tarry feces that are commonly associated with upper gastrointestinal bleeding. [1] The black color and characteristic strong odor are caused by hemoglobin in the blood being altered by digestive enzymes and intestinal bacteria .
Blood in stool looks different depending on how early it enters the digestive tract—and thus how much digestive action it has been exposed to—and how much there is. The term can refer either to melena, with a black appearance, typically originating from upper gastrointestinal bleeding; or to hematochezia, with a red color, typically originating from lower gastrointestinal bleeding. [6]
An upper GI bleed is more common than lower GI bleed. [2] An upper GI bleed occurs in 50 to 150 per 100,000 adults per year. [8] A lower GI bleed is estimated to occur in 20 to 30 per 100,000 per year. [2] It results in about 300,000 hospital admissions a year in the United States. [1] Risk of death from a GI bleed is between 5% and 30%.
Persons with upper gastrointestinal bleeding often present with hematemesis, coffee ground vomiting, melena, or hematochezia (maroon-coloured stool) if the hemorrhage is severe. The presentation of bleeding depends on the amount and location of hemorrhage.
A lower gastrointestinal bleed is defined as bleeding originating distal to the ileocecal valve, which includes the colon, rectum, and anus. [2] LGIB was previously defined as any bleed that occurs distal to the ligament of Treitz, which included the aforementioned parts of the intestine and also included the last 1/4 of the duodenum and the entire area of the jejunum and ileum. [1]
Hematemesis, melena, and hematochezia are symptoms of acute gastrointestinal bleeding. Bleeding that brings the patient to the physician is a potential emergency and must be considered as such until its seriousness can be evaluated.
For example, bloody vomit or melena, black tarry stools, usually indicate a gastrointestinal bleed from a location in the upper gastrointestinal tract. In contrast, hematochezia, bright red blood or clots in the stool, usually indicates gastrointestinal bleeding from the lower part of the gastrointestinal tract. [6]
Fecal occult blood testing (FOBT), as its name implies, aims to detect subtle blood loss in the gastrointestinal tract, anywhere from the mouth to the colon.Positive tests ("positive stool") may result from either upper gastrointestinal bleeding or lower gastrointestinal bleeding and warrant further investigation for peptic ulcers or a malignancy (such as colorectal cancer or gastric cancer).