What is gastrointestinal bleeding? Gastrointestinal bleeding is bleeding that occurs anywhere in the digestive tract, also called the gastrointestinal tract, which runs from the mouth to the anus. Blood may be present in vomit or stool. Depending on where the bleeding originates, the blood may be visible or occult, which means that it can be detected only by laboratory testing. The severity of gastrointestinal bleeding varies among individuals depending on the cause. Fresh blood in vomit (hematemesis) suggests lesions in the esophagus (varices). Coffee ground-appearing blood in vomit typically indicates stomach ulcer. Typically, bleeding from the upper gastrointestinal tract that ‘heads downstream’ manifests as black or tarry stool known as melena. The black color develops because of chemical changes that occur as the blood passes through the digestive tract. The passage of bright red blood from the anus is known as hematochezia and usually results from bleeding from sources that are closer to the anus and rectum. Common causes of gastrointestinal bleeding are inflammation and infections in the digestive tract, such as gastritis. Mild gastrointestinal bleeding is common with viral infections, and this bleeding will go away as the infection resolves. People with an anal fissure or hemorrhoids may also have mild bleeding that resolves on its own. If severe bleeding occurs, it can result in significant blood loss, leading to symptoms such as lightheadedness, dizziness, fainting, or difficulty breathing. While gastrointestinal bleeding can be minor, it can also result from severe conditions that are characterized by prolonged bleeding. In these cases, serious complications such as shock can develop. Gastrointestinal bleeding can also occur from cancers in the digestive tract. Left untreated, severe gastrointestinal bleeding can result in a life-threatening loss of blood. Seek immediate medical care (call 911) for serious symptoms, pale skin or pallor and difficulty breathing, severe abdominal pain, vomiting blood or black material, or change in level of consciousness.