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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.
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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]
Digested blood from the upper gastrointestinal tract may appear black rather than red, resulting in "coffee ground" vomit or melena. [2] Other signs and symptoms include feeling tired, dizziness, and pale skin color. [18] A number of foods and medications can turn the stool either red or black in the absence of bleeding. [2]
Human feces photographed in a toilet, shortly after defecation.. Human feces (American English) or faeces (British English), commonly and in medical literature more often called stool, [1] are the solid or semisolid remains of food that could not be digested or absorbed in the small intestine of humans, but has been further broken down by bacteria in the large intestine.
The strongest predictors of an upper gastrointestinal bleed are black stool, age <50 years, and blood urea nitrogen/creatinine ratio 30 or more. [8] [9] The diagnosis of upper gastrointestinal bleeding is assumed when hematemesis (vomiting of blood) is observed. [citation needed]
Hematochezia is a form of blood in stool, in which fresh blood passes through the anus while defecating. It differs from melena, which commonly refers to blood in stool originating from upper gastrointestinal bleeding (UGIB). [1] The term derives from Greek αἷμα ("blood") and χέζειν ("to defaecate").
Perianal hematoma are caused by the rupture of a small vein that drains blood from the anus. [4] This rupture may be the result of forceful or strained bowel movement, anal sex or caused by heavy lifting, coughing or straining.