Black, tarry stools with a foul odor can be the result of eating certain foods, taking iron supplements, or possibly from internal bleeding. If the black color is from blood, it is known as "melena." The color indicates that the blood has been in the body for some time, and is coming from higher up in the gastrointestinal tract.
False Melana
A black stool caused by food, supplements, medication, or minerals is known as "false melena." Iron supplements, taken alone or as part of a multivitamin for iron-deficient anemia, may cause stools to be black or even greenish in color. Foods that are dark blue or black in color may also cause black stools. Substances that can cause false melena are:
- Black licorice
- Blueberries
- Iron supplements
- Lead
- Bismuth (Pepto-bismol)
A physician should be consulted immediately if black stools can not be attributed to a benign cause such as an iron supplement or a food.
Diagnosing Melena
The black color alone is not enough to determine that it is blood that is being passed in the stool. Therefore, a physician may order a fecal occult blood (FOBT) test to measure the amount of blood. An FOBT is a simple test for a patient—it only requires that a stool sample be collected at home and dropped off at the physician’s office or a laboratory. Melena is diagnosed if 6 tablespoons (200 milliliters) of blood or more is found in the stool passed.
The blood could be caused by several different conditions including a bleeding ulcer, gastritis, esophageal varices or a tear in the esophagus from violent vomiting (Mallory-Weiss tear). The tarry appearance of the stool is from the blood having contact with the body’s digestive juices.
After melena is diagnosed, a physician may order other diagnostic tests to determine the cause and exact location of the bleeding. This could include x-rays, blood tests, colonoscopy, gastroscopy, stool culture, and barium studies.
Causes of Melena
Bleeding ulcer. An ulcer is a type of sore on the lining of the stomach which can cause bleeding and result in melena. Contrary to popular belief, stomach ulcers are not usually caused by stress or spicy food (although these can aggravate an already existing ulcer). In fact, they are typically caused by an infection with a bacterium called Helicobacter pylori (H. pylori). Antibiotics are normally prescribed to eliminate the infection.
Another cause of stomach ulcers is the prolonged use of pain medications known as NSAIDs (nonsteroidal anti-inflammatory drugs). NSAIDs can irritate the stomach by weakening the ability of the lining to resist acid made in the stomach. For this same reason, NSAIDs have an adverse effect on Crohn's disease and ulcerative colitis. NSAIDs include common over the counter drugs such as ibuprofen, naproxen sodium, and aspirin. Stomach ulcers caused by NSAIDs usually heal after the offending drug is discontinued.
Gastritis. Gastritis is the inflammation of the stomach lining and can be caused by overindulging in alcohol or food, eating spicy foods, smoking, infection with bacteria or prolonged use of NSAIDs. Gastritis can also develop after surgery or trauma, or be associated with already existing medical conditions.
Esophageal varices. Esophageal varices are dilated veins located in the wall of the lower esophagus or upper stomach. When these veins rupture they may cause blood to appear in the stool or vomit. Esophageal varices are a serious complication resulting from portal hypertension brought on by cirrhosis of the liver.
Mallory-Weiss tear. A tear in the mucous membrane that joins the esophagus and the stomach may bleed and result in melena. This condition is fairly rare (occurring in 4 of 100,000 people), and may be caused by violet vomiting, coughing, or epileptic convulsions.
