Blood in the stool is a common cause of dark stools, and can get into stools through internal bleeding in one of the organs of the digestive system. Blood then enters the alimentary canal, the space in which food is processed, and mixes with chyme, which is partially digested food. The mixture of blood and chyme results in dark, and sometimes black, stool. Although there are other causes, blood remains the main cause of dark stools.
Ulcer
Dark stool may be caused by a bleeding ulcer. An ulcer, a type of sore, can form on the stomach lining and bleed, causing blood to pass through the digestive tract. In the intestine, the blood mixes with fecal matter, resulting in darker stool. According to "Harrison's Principles of Internal Medicine," Helicobacter pylori, or H. pylori, commonly cause stomach ulcers. Since H. pylori is a type of bacteria, treating stomach ulcers may involve antibiotics to eliminate bacterial infection.
Stomach ulcers may also be caused by nonsteroidal anti-inflammatory drugs, or NSAIDs, such as ibuprofen, aspirin and naproxen sodium. According to the National Digestive Diseases Information Clearinghouse, ulcers can be healed with proton pump inhibitors, or PPIs; histamine receptor blockers, or H2 blockers; and discontinuation of NSAIDs.
Gastritis
Stomach ulcers may be due to stomach lining inflammation called gastritis. Smoking, bacterial infection, NSAIDs or certain foods can lead to gastritis. Alcohol prompts the stomach to increase acid secretion, wearing away at the stomach lining. In addition, gastritis may be linked to an existing medical condition, such as anemia, lupus, rheumatoid arthritis and hypothyroidism.
Several treatment options are available for gastritis. Certain medications can reduce stomach acids, allowing the lining to heal. Antibiotics may be used if bacterial infection is present. Discontinuing NSAIDs would also allow the lining to repair itself.
Other Causes
Aside from ulcers and gastritis, other causes of dark stool include the Mallory-Weiss tear and esophageal varices. The Mallory-Weiss tear is a lesion of the mucosal membrane between the esophagus and stomach; blood enters the alimentary canal at the site of this lesion. Although rare, this condition may result in epileptic convulsions, regurgitating and painful coughing.
When veins dilate in the esophagus and stomach wall, esophageal varices may result if the vein ruptures. The blood from the ruptured vein enters the stomach and eventually causes dark stool. This serious complication is due to cirrhosis of the liver.
In addition to blood, dark stool may also be caused by bismuth, iron, charcoal, dark foods and constipation.
References
- "Harrison's Principals of Internal Medicine"; Fauci, Braunwald, Kasper, Hauser, Longo, Jameson and Loscalzo; 2008
- Jackson Siegelbaum Gastroenterology: Gastritis
- National Digestive Diseases Information Clearinghouse: NSAIDs and Peptic Ulcers
