Melena
Encyclopedia
In medicine
, melena or melaena refers to the black, "tarry" feces
that are associated with gastrointestinal hemorrhage. The black color is caused by oxidation of the iron
in hemoglobin
during its passage through the ileum
and colon
.
and rectum
) is generally associated with the passage of bright red blood, or hematochezia
, particularly when brisk. Blood acts as a cathartic agent in the intestine, promoting its prompt passage. Only blood that originates from a high 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 tract), 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. 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.
or those due to low blood pressure. Very often, however, aside from the melena itself, there are no other symptoms. The presence of blood must be confirmed with either a positive hemoccult slide on rectal exam, frank blood on the examining finger, or a positive stool guaiac from the lab. If a source in the upper GI tract is suspected, an upper endoscopy can be performed to diagnose the cause.
Lower GI 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. Note: As iron is the source of the black color, consumption of black pudding may cause asymptomatic melena.
disease. Any other cause of bleeding from the upper gastro-intestinal tract, or even the ascending colon, can also cause melena. Melena may also be a sign of drug overdose if a patient is taking anti-coagulants, such as warfarin. It is also caused by tumours, especially malignant tumors affecting the esophagous, more commonly the stomach & less commonly the small intestine due to their bleeding surface. However,the most prominent and helpful sign in these cases of malignant tumours is haematemesis. It may also accompany hemorrhagic blood diseases (e.g. purpura
& hemophilia). Other medical causes of melena include bleeding ulcers, gastritis
, esophageal varices
, and Mallory-Weiss syndrome
.
Some 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 the traditional African Maasai diet, which includes much blood drained from cattle.
Melena is usually not a medical emergency
because the bleeding is slow. Urgent care however 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.
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, melena or melaena refers to the black, "tarry" feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
that are associated with gastrointestinal hemorrhage. The black color is caused by oxidation of the iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
in hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
during its passage through the ileum
Ileum
The ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum.The ileum follows the duodenum...
and colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
.
Melena vs. hematochezia
Bleeding originating from the lower GI tract (such as the sigmoid colonSigmoid colon
The sigmoid colon is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about 40 cm...
and rectum
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
) is generally associated with the passage of bright red blood, or hematochezia
Hematochezia
Hematochezia is the passage of fresh blood per anus, usually in or with stools . Hematochezia is commonly associated with lower gastrointestinal bleeding, but may also occur from a brisk upper GI bleed...
, particularly when brisk. Blood acts as a cathartic agent in the intestine, promoting its prompt passage. Only blood that originates from a high source (such as the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
), 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
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
in the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
or duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
(upper gastrointestinal tract), for example by a peptic ulcer
Peptic ulcer
A peptic ulcer, also known as PUD or peptic ulcer disease, is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. It is defined as mucosal erosions equal to or greater than 0.5 cm...
. 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. One often-stated rule of thumb is that melena only occurs if the source of bleeding is above the ligament of Treitz
Suspensory muscle of the duodenum
The Suspensory muscle of duodenum or Ligament of Treitz connects the duodenum of the small intestines to the diaphragm. It contains a slender band of skeletal muscle from the diaphragm and a fibromuscular band of smooth muscle from the horizontal and ascending parts of the duodenum...
although, as noted below, exceptions occur with enough frequency to render it unreliable.
Diagnosis
Patients sometimes present with signs of anemiaAnemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
or those due to low blood pressure. Very often, however, aside from the melena itself, there are no other symptoms. The presence of blood must be confirmed with either a positive hemoccult slide on rectal exam, frank blood on the examining finger, or a positive stool guaiac from the lab. If a source in the upper GI tract is suspected, an upper endoscopy can be performed to diagnose the cause.
Lower GI 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. Note: As iron is the source of the black color, consumption of black pudding may cause asymptomatic melena.
Causes
The most common cause of melena is peptic ulcerPeptic ulcer
A peptic ulcer, also known as PUD or peptic ulcer disease, is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. It is defined as mucosal erosions equal to or greater than 0.5 cm...
disease. Any other cause of bleeding from the upper gastro-intestinal tract, or even the ascending colon, can also cause melena. Melena may also be a sign of drug overdose if a patient is taking anti-coagulants, such as warfarin. It is also caused by tumours, especially malignant tumors affecting the esophagous, more commonly the stomach & less commonly the small intestine due to their bleeding surface. However,the most prominent and helpful sign in these cases of malignant tumours is haematemesis. It may also accompany hemorrhagic blood diseases (e.g. purpura
Purpura
Purpura is the appearance of red or purple discolorations on the skin that do not blanch on applying pressure. They are caused by bleeding underneath the skin...
& hemophilia). Other medical causes of melena include bleeding ulcers, gastritis
Gastritis
Gastritis is an inflammation of the lining of the stomach, and has many possible causes. The main acute causes are excessive alcohol consumption or prolonged use of nonsteroidal anti-inflammatory drugs such as aspirin or ibuprofen. Sometimes gastritis develops after major surgery, traumatic...
, esophageal varices
Esophageal varices
In medicine , esophageal varices are extremely dilated sub-mucosal veins in the lower esophagus...
, and Mallory-Weiss syndrome
Mallory-Weiss syndrome
Mallory–Weiss syndrome or gastro-esophageal laceration syndrome refers to bleeding from tears in the mucosa at the junction of the stomach and esophagus, usually caused by severe retching, coughing, or vomiting.-Causes:...
.
Some causes of "false" melena include Iron supplements
Iron supplements
Iron supplements are supplements that can be prescribed by a doctor for a medical reason. Iron can also be a dietary supplement, which can be purchased in supermarkets etc. These two categories should not be confused....
, Pepto-Bismol
Pepto-Bismol
Pepto-Bismol is an over-the-counter drug currently produced by the Procter and Gamble company in the United States of America and in Canada to treat minor digestive system upset. Its active ingredient is bismuth subsalicylate...
, Maalox
Maalox
Maalox is a brand name antacid containing aluminium hydroxide and magnesium hydroxide to neutralize or reduce stomach acid.Maalox helps relieve symptoms of excessive stomach acidity in patients with indigestion, heartburn, gastroesophageal reflux disease, or stomach or duodenal ulcers. In large...
, and lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, blood swallowed as a result of a nose bleed (epistaxis), and blood ingested as part of the diet, as with the traditional African Maasai diet, which includes much blood drained from cattle.
Melena is usually not a medical emergency
Medical emergency
A medical emergency is an injury or illness that is acute and poses an immediate risk to a person's life or long term health. These emergencies may require assistance from another person, who should ideally be suitably qualified to do so, although some of these emergencies can be dealt with by the...
because the bleeding is slow. Urgent care however 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.