Common Causes of Blood in Diarrhea

Bloody diarrhea represents a double abnormality. Diarrhea is defined as an excessive volume of stool, while blood in stool is never normal. The responsible diseases range from relatively mild infections that typically get better with minimal treatment to conditions that may be life-threatening. While some causes are less serious than others, only your doctor can make that determination. Early consultation may be life-saving.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.


Many infectious organisms can cause bloody diarrhea. Contaminated meats -- particularly ground meats that weren't cooked thoroughly -- and improperly prepared vegetables are the most common sources of foodborne intestinal infections. Additionally, even the brief use of an antibiotic may lead to the overgrowth of resistant germs and bloody diarrhea. Treatment depends upon accurate identification of the infecting organism, and can range from intravenous fluids and antibiotics to surgical removal of part of the bowel.

Inflammatory Bowel Disease

Ulcerative colitis (UC) and Crohn disease are chronic inflammatory diseases of the intestinal tract that frequently produce bloody diarrhea as a first symptom. Diagnosis is made by inspecting the lining of the bowel with x-rays or a flexible scope. The causes of inflammatory bowel disease are complex and not fully understood. They include genetic predisposition, lifestyle factors, environmental influences, infectious agents and disorders of the immune system. UC affects only the colon. Crohn disease involves both the small and large intestine. UC may be managed medically, and can be cured by removing the large intestine. Crohn disease is incurable but can be managed with medication and changes in diet and lifestyle.

Cancer of the Colon and Rectum

Cancer can occur in any part of the intestinal tract. The closer the tumor is to the rectum, the more likely it is to cause bright red bleeding. Diagnosis requires a barium enema x-ray or examination with a flexible scope inserted into the digestive tract. According to the National Cancer Institute, 90.1 percent of those diagnosed with cancer of the colon and rectum before spread to lymph nodes has occurred will be alive, disease-free and considered cured 5 years after treatment. Spread to the lymph nodes reduces the 5-year cure rate to 71.2 percent, and only 13.5 percent of those with spread beyond the lymph nodes will be alive at 5 years. Prompt medical consultation for bloody stools is essential.

Upper and Middle Digestive Tract Diseases

The longer blood is in the intestinal system, the more likely it is to turn dark or tarry in appearance when it is expelled with stool. That rule is not absolute, however, and upper and middle digestive tract bleeding that is serious enough to cause diarrhea may pass quickly enough to remain bright red. Possible causes include peptic ulcers, cancer of the stomach or small intestine, blood vessel malformations and severe liver disease. A rare cause is the rupture of an aneurysm -- abnormal enlargement of an artery -- into the intestine. This condition may be signaled by a so-called sentinel bleed that stops on its own before complete and potentially life-threatening rupture occurs.

Warnings and Precautions

Seek urgent medical attention if you experience bloody diarrhea. Emergency care is necessary if you experience signs or symptoms of dehydration or critical blood loss, including: -- increased thirst or dry mouth -- dark urine or decreased urination -- lightheadedness, dizziness or fainting -- fast or irregular heartbeat -- confusion, anxiety or sluggishness -- blue discoloration of the lips or fingernails

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