Blood in stool is an indication of a problem somewhere in the gastrointestinal (GI) tract, anywhere between the mouth and anus. According to MedlinePlus, the blood may be red, maroon or black, but it is frequently not visible and can only be detected through a fecal occult blood test.

Upper GI Tract

MedlinePlus indicates that stools that contain blood from the upper GI tract are typically black and sometimes tarry. Causes can include a bleeding ulcer, gastritis (stomach inflammation), a tear in the esophagus, an abnormality in blood vessels, trauma or a foreign object.

Lower GI Tract

Red or maroon blood in stool is indicative of a problem in the lower GI tract, such as hemorrhoids, inflammatory bowel disease (Crohn's disease or ulcerative colitis), a small bowel tumor, diverticulosis, anal fissures, colon polyps or colon cancer, according to MedlinePlus.

Severe Bleeding

Excessive bleeding in the GI tract can cause you to vomit blood and produce bright red blood in your stool. In some cases, emergency medical care is needed.

Diagnosis

According to MedlinePlus, the specific condition causing blood in stool can be diagnosed by X-rays, endoscopy, colonoscopy, barium studies, blood tests, a stool culture and angiography, along with a physical examination and consideration of your medical history.

Considerations

Certain foods can cause black stools, such as iron pills, black licorice, blueberries and bismuth medicines (such as Pepto-Bismol), according to MedlinePlus. In addition, foods such as tomatoes and beets can cause reddish-colored stools.

Source:

MedlinePlus: Bloody or Tarry Stools