Bloody stools often indicate an injury or disorder in the digestive tract. Your doctor may use the term "melena" to describe black, tarry, and foul-smelling stools or "hematochezia" to describe red- or maroon-colored stools.

Blood in the stool may come from anywhere along your digestive tract, from mouth to anus. It may be present in such small amounts that you cannot actually see it, but is only detectable by a fecal occult blood test. When there IS enough blood to change the appearance of your stools, the doctor will want to know the exact color to help find the site of bleeding. To make a diagnosis, your doctor may use endoscopy or special x-ray studies.

A black stool usually means that the blood is coming from the upper part of the gastrointestinal (GI) tract. This includes the esophagus, stomach, and the first part of the small intestine. Blood will typically look like tar after it has been exposed to the body's digestive juices. Stomach ulcers caused by ibuprofen, naproxen, or aspirin are common causes of upper GI bleeding.

Maroon-colored stools or bright red blood usually suggest that the blood is coming from the lower part of the GI tract (large bowel or rectum). Hemorrhoids and diverticulitis (inflammation of an abnormal pouch in the colon) are the most common causes of lower GI bleeding. However, sometimes massive or rapid bleeding in the stomach causes bright red stools.

Consuming black licorice, lead, iron pills, bismuth medicines like Pepto-Bismol, or blueberries can also cause black stools. Beets and tomatoes can sometimes make stools appear reddish. In these cases, your doctor can test the stool with a chemical to rule out the presence of blood.

Brisk bleeding in the esophagus or stomach (such as with peptic ulcer disease), can also cause you to vomit blood.

Upper GI tract (usually black stools):

• Bleeding stomach or duodenal ulcer
• Gastritis
• Esophageal varices
• Mallory-Weiss tear (a tear in the esophagus from violent vomiting)
• Trauma or foreign body
• Bowel ischemia (a lack of proper blood flow to the intestines)
• Vascular malformation

Lower GI tract (usually maroon or bright red, bloody stools):

• Hemorrhoids
• Anal fissures
• Diverticular bleeding
• Intestinal infection (such as bacterial enterocolitis)
• Vascular malformation
• Inflammatory bowel disease
• Tumor
• Colon polyps or colon cancer
• Trauma or foreign body
• Bowel ischemia (a lack of proper blood flow to the intestines)

Green BT, Tendler DA. Ischemic Colitis: A Clinical Review. South Med J. 2005; 98 (2): 217-222.

Cappell MS. The role of sigmoidoscopy and colonoscopy in the diagnosis and management of lower gastrointestinal disorders: technique, indications, and contraindications. Med Clin North Am. 2002; 86(6): 1217-1252.