What Causes Blood Clots in Stools?

Bleeding from various places in the digestive tract presents in different ways. The presence of blood clots in the stool usually signals bleeding from the colon, also known as the large intestine or large bowel. The stool might also appear maroon with bleeding in the colon. Various medical conditions can cause bleeding in the large intestine. Seek urgent medical care if you notice blood clots in your stool.

Diverticular Bleeding

A complication of diverticulosis called diverticular bleeding is the most common cause of large bowel bleeding. With diverticulosis, small bulges or outpouchings called diverticuli form in areas where the colon wall is weak. Diverticuli do not cause symptoms in and of themselves but bleeding is a possible complication. As noted in the medical text Mayo Clinic Gastroenterology and Hepatology Board Review, 5th Edition, this type of bleeding occurs in approximately 3 to 5 percent of people with diverticulosis 5.

Diverticular bleeding is characteristically painless except perhaps some lower abdominal cramps followed by an urgent need to have a bowel movement. Stools during a diverticular bleed are usually red or maroon and often contain blood clots. Diverticulosis and diverticular bleeding occur most often in people older than age 50. However, both conditions can occur in younger adults. Although diverticular bleeding often stops on its own, urgent medical care is necessary as potentially life-threatening blood loss can occur.

Colitis

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Colitis is a general term that refers to inflammation of the colon, which can be temporary or ongoing (chronic) depending on the underlying cause. Bleeding from the colon is a common symptom with various types of colitis, usually leading to bloody diarrhea that might contain clots.

Infectious Colitis

Infectious colitis typically develops due to bacterial, parasitic, or fungal food poisoning. In the United States, infectious colitis is most often caused by a bacterial infection. Possible culprits include certain strains of E. coli, Salmonella, Shigella and Campylobacter, among others. Abdominal pain, fever, nausea and other digestive system symptoms frequently accompany these infections.

Ischemic Colitis

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Ischemic colitis refers to a temporary disruption of blood flow to part of the colon, which damages the affected area. This leads to sudden abdominal pain and cramps, and often the urgent need to have a bowel movement. Nausea, vomiting and abdominal bloating also frequently occur. Passage of bloody stool that might contain clots often follows within 24 hours. A variety of underlying conditions can lead to ischemic colitis, ranging from atherosclerosis to sickle cell disease to heart failure, among others. Older adults are more commonly affected by ischemic colitis than younger adults.

Inflammatory Bowel Disease

Crohn disease and ulcerative colitis are chronic inflammatory bowel diseases caused by an abnormal immune system response. Bleeding from the colon is common during a disease flareup with ulcerative colitis and blood clots might appear in the stool. This type of bleeding is uncommon with Crohn disease unless the area of inflammation is confined to the colon. Unlike ischemic colitis, inflammatory bowel disease most often develops during late adolescence or early adulthood.

Other Causes

Several other diseases and conditions can cause digestive tract bleeding and blood clots in the stool. Dilated blood vessels in the colon, known as vascular ectasias, can rupture and bleed. This condition occurs most commonly in people older than age 60. Growths in the colon called polyps and colon cancer also sometimes bleed enough to cause visible clots in the stool. Bleeding might also occur after removal of a colon polyp.

While blood clots in the stool most often signal bleeding from the colon, this symptom uncommonly occurs with a sizable bleed from higher in the digestive tract. Some of the more common causes of bleeding from the upper digestive tract include severe peptic ulcer disease and ruptured stomach or esophageal varices -- engorged, dilated veins.

Warnings and Precautions

Blood clots in the stool indicate significant bleeding from you digestive tract, which requires immediate medical evaluation and treatment. Seek emergency care if you experience any of these additional warning signs and symptoms:

• vomiting blood
  
• dizziness or fainting
• rapid pulse
• cold, clammy skin
• high fever
• severe or worsening abdominal pain

Reviewed and revised by: Tina M. St. John, M.D.