There are 17 possible causes of black stools
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Bloody or tarry stools refer to a stool sample that is either dark red or black in color. Bloody or tarry stools can indicate bleeding or other injuries in your gastrointestinal tract. You may also have dark, discolored bowel movements after eating dark-colored foods. Notify your doctor any time you have bloody or black-colored stool to rule out serious medical conditions.
Bleeding in the upper portion of your digestive system can cause black, tarry stools. Ulcers or another form of irritation in your esophagus or stomach known as gastritis can cause bleeding. When the blood mixes with digestive fluids, it takes on the appearance of tar.
Certain medications can also lead to black-colored stools. Iron supplements and bismuth-based medications, for example, can darken your stools.
Sometimes, serious blood and circulation abnormalities in your digestive system can cause black, tarry stools. These include:
- bowel ischemia: a reduction of blood flow to the intestines
- vascular malformation: misshapen veins
- varices: large protruding veins in the intestines
Red or bloody stools can also be caused by several different medical conditions. Your stools may be bloody due to bleeding in the lower half of your digestive system. Cancerous or benign polyps on your colon can produce gastrointestinal bleeding in some cases. Inflammatory bowel diseases such as diverticulosis, ulcerative colitis, and Crohn’s disease may cause you to expel bright red or maroon-colored blood in your stool.
A common cause of blood stools is the presence of hemorrhoids. Hemorrhoids are swollen veins located in your rectum or anus. Straining to produce a bowel movement can cause bleeding.
Blockages at any point in your digestive tract can cause black, tarry, or bloody stools.
The foods you eat can cause your stools to appear bloody or tarry. Eating red or black foods can give your feces a dark appearance without the existence of blood. Black licorice, blueberries, dark chocolate cookies, red-colored gelatin, beets, or red fruit punch are all examples of foods that can discolor your bowel movements.
Your doctor will take a medical history and perform a physical examination to determine the cause of your unusual stool color. Imaging tests such as MRIs, X-rays, and CT scans can help your doctor see the blood flow to your digestive system. These diagnostic tools will reveal any blockages that could be causing gastrointestinal (GI) bleeding.
Your doctor may schedule a colonoscopy to assess the condition of your colon. A colonoscopy is often performed under sedation. Your doctor will use a thin, flexible tube with a camera on the end to see the inside of your colon and look for the cause of your symptoms.
Treatment of bloody or tarry stools varies according to the cause of the problem. According to the American Cancer Society, people that have hemorrhoids can ease the passage of stool and reduce bleeding by using stool softeners under a doctor’s direction (ACS). Sitz baths can also ease the pain of hemorrhoids and prevent bleeding.
Your doctor may prescribe acid-reducing medications to treat bleeding ulcers, or antibiotics and immunosuppressant drugs to calm inflammatory bowel disease and infections.
Vein abnormalities and blockages may require surgical repair if the bleeding does not stop on its own. If you have lost a lot of blood through your stool, you may be at risk for developing anemia. You may need a blood transfusion to replenish your supply of red blood cells.
Polyps on your colon that cause bloody stools can indicate precancerous conditions or cancer in some people. Your doctor will determine the appropriate treatment for these conditions. Removal of the polyps may be all that is needed in some cases. Others may require radiation therapy and chemotherapy if cancer is present.
- Blood in stool. (n.d.). American Cancer Society. Retrieved July 3, 2012, from http://www.cancer.org/Treatment/TreatmentsandSideEffects/PhysicalSideEffects/DealingwithSymptomsatHome/caring-for-the-patient-with-cancer-at-home-blood-in-stool
- Bloody or tarry stools. (n.d.). National Library of Medicine - National Institutes of Health. Retrieved July 3, 2012, from http://www.nlm.nih.gov/medlineplus/ency/article/003130.htm
- Gastrointestinal bleeding (n.d.). National Library of Medicine - National Institutes of Health. Retrieved July 3, 2012, from http://www.nlm.nih.gov/medlineplus/ency/article/003133.htm
- Stool color: When to worry. (n.d.). Mayo Clinic. Retrieved July 3, 2012, from http://www.mayoclinic.com/health/stool-color/an00772
Possible Causes - Listed in order from the most common to the least.
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