GI bleeding is not a disease, but a symptom of a disease. There are many possible causes of GI bleeding, including hemorrhoids, peptic ulcers, tears or inflammation in the esophagus, diverticulosis and diverticulitis, ulcerative colitis and Crohn's disease, colonic polyps, or cancer in the colon, stomach or esophagus.
The test used most often to look for the cause of GI bleeding is called endoscopy. It uses a flexible instrument inserted through the mouth or rectum to view the inside of the GI tract. A type of endoscopy called colonoscopy looks at the large intestine.