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|Classification and external resources|
|Specialty||General surgery, gastroenterology|
In medicine, melena or melæna refers to the black "tarry" feces that are associated with upper gastrointestinal bleeding. The black color is caused by the hemoglobin in the blood being altered by digestive chemicals and intestinal bacteria.
The origin of melena is dated to the early 19th century via modern Latin, via Greek melaina (feminine of melas, black).
The most common cause of melena is peptic ulcer disease. Any other cause of bleeding from the upper gastrointestinal tract or even the ascending colon can also cause melena. Melena may also be a sign of drug overdose if a patient is taking anticoagulants, such as warfarin. It is also caused by tumors, especially malignant tumors affecting the esophagus, more commonly the stomach and less commonly the small intestine due to their bleeding surface. However, the most prominent and helpful sign in these cases of malignant tumors is haematemesis. It may also accompany hemorrhagic blood diseases (e.g. purpura and hemophilia). Other medical causes of melena include bleeding ulcers, gastritis, esophageal varices, Meckel's diverticulum and Mallory-Weiss syndrome.:320–321
Causes of "false" melena include iron supplements, Pepto-Bismol, Maalox, and lead, blood swallowed as a result of a nose bleed (epistaxis), and blood ingested as part of the diet, as with consumption of black pudding (blood sausage), or with the traditional African Maasai diet, which includes much blood drained from cattle.
Melena is often a medical emergency as it arises from a significant amount of bleeding. Urgent care is required to rule out serious causes and prevent potentially life-threatening emergencies.
A less serious, self-limiting case of melena can occur in newborns two to three days after delivery, due to swallowed maternal blood.
In acute cases, with a large amount of blood loss, patients may present with anemia or low blood pressure. However, aside from the melena itself, many patients may present with few symptoms. Often, the first approach is to use endoscopy to look for obvious signs of a bleed. In cases where the source of the bleed is unclear, but melena is present, an upper endoscopy is recommended, to try to ascertain the source of the bleed.
Lower gastrointestinal bleeding sources usually present with hematochezia or frank blood. A test with poor sensitivity/specificity that may detect the source of bleeding is the tagged red blood cell scan. This is especially used for slow bleeding (<0.5 ml/min). However, for rapid bleeding (>0.5 ml/min), mesenteric angiogram ± embolization is the gold standard. Colonoscopy is often first line, however.
Melena versus hematochezia
Bleeds that originate from the lower gastrointestinal tract (such as the sigmoid colon and rectum) are generally associated with the passage of bright red blood, or hematochezia, particularly when brisk. Only blood that originates from a more proximal source (such as the small intestine), or bleeding from a lower source that occurs slowly enough to allow for enzymatic breakdown, is associated with melena. For this reason, melena is often associated with blood in the stomach or duodenum (upper gastrointestinal bleeding), for example by a peptic ulcer. A rough estimate is that it takes about 14 hours for blood to be broken down within the intestinal lumen; therefore if transit time is less than 14 hours the patient will have hematochezia, and if greater than 14 hours the patient will exhibit melena.:322 One often-stated rule of thumb is that melena only occurs if the source of bleeding is above the ligament of Treitz although, as noted below, exceptions occur with enough frequency to render it unreliable.
- MedlinePlus Encyclopedia Bloody or tarry stools, retrieved 19 July 2010.
- Navarra, Tova (2004). The Encyclopædia of Vitamins, Minerals, and Supplements. Infobase Publishing.
Iron supplements cause a grayish-black stool that should be distinguished from the black, tarlike stool that occurs from bleeding ulcer.
- Walker, HK; Hall, WD; Hurst, JW (1990). Clinical Methods: The History, Physical, and Laboratory Examinations.
Melena strongly suggests, and hematemesis confirms, that bleeding is of upper gastrointestinal origin…Peptic ulcer, the most common cause of gastrointestinal hemorrhage, should be pursued through questions about epigastric distress, the relationship of symptoms to food intake, and a past history of peptic ulcer disease..
- Laine, Loren (2012). "41. Gastrointestinal Bleeding". In Longo, Dan L; Fauci, Anthony S; Kasper, Dennis L; Hauser, Stephen L; Jameson, J. Larry; Loscalzo, Joseph. Harrison's principles of internal medicine (18th ed.). New York: McGraw-Hill. ISBN 978-0-07-174889-6.