Gastrointestinal bleeding can range from microscopic bleeding, where the amount of blood is so small that it can only be detected by laboratory testing (in the form of iron deficiency anemia), to massive bleeding where pure blood is passed and hypovolemia and shock may develop, risking death.
Gastrointestinal bleeding can be roughly divided into two clinical syndromes.
Upper gastrointestinal bleeding
Upper gastrointestinal bleeding is from a source between the pharynx and the ligament of Treitz. An upper source is characterised by hematemesis (vomiting up blood) and melena (tarry stool containing altered blood).
Lower gastrointestinal bleeding
Lower gastrointestinal bleeding may be indicated by red blood ''per rectum'', especially in the absence of hematemesis. Isolated melena may originate from anywhere between the stomach and the proximal colon.
Further Reading
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"Gastrointestinal bleeding"
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