Gastrointestinal bleeding refers to any bleeding that starts in the gastrointestinal tract, which extends from the mouth to the large bowel. The amount of bleeding can range from nearly undetectable to acute, massive, and life threatening. Bleeding may come from any site along the gastrointestinal tract, but is often divided into:

• Upper GI bleeding: The upper gastrointestinal (GI) tract is located between the mouth and outflow tract of the stomach.
• Lower GI bleeding: The lower GI tract is located from the outflow tract of the stomach to the anus (small and large bowel included).

Gastrointestinal bleeding can range from microscopic bleeding (the amount of blood is so small that it can only be detected by laboratory testing) to massive bleeding (pure blood is passed).

It is important to be aware of gastrointestinal bleeding, because it may point to many significant diseases and conditions. Prolonged microscopic bleeding can lead to massive loss of iron, causing anemia. Acute, massive bleeding can lead to hypovolemia, shock, and even death.

Gastrointestinal bleeding can occur at any age from birth on. The degree and suspected location of the bleeding determines what tests should be performed to find the cause. Once a bleeding site is identified, many therapies are available to stop the bleeding.

Some of the possible causes of gastrointestinal bleeding include:

• Hemorrhoids
• Duodenal ulcer
• Gastric (stomach) ulcer
• Bleeding diverticulum
• Ulcerative colitis
• Crohn's disease
• Esophageal varices
• Arterio-venous malformations
• Nosebleed
• Mallory-Weiss tear (tear in esophagus after vomiting)
• Esophagitis
• Dysentery (bloody, infectious diarrhea)
• Ischemic bowel
• Colon cancer
• Intestinal polyps
• Celiac sprue
• Radiation injury to the bowel
• Portal hypertensive gastropathy
• Stomach cancer
• Intestinal vasculitis
• Small intestinal cancer
• Dieulafoy's lesion
• Meckel's diverticulum
• Aorto-enteric fistula
• Cow's milk allergy
• Intestinal obstruction (twisted bowel)
• Intussusception (bowel telescoped on itself)
• Anal fissure

There are home stool tests for microscopic blood that may be recommended for people with anemia or for colon cancer screening.