In
medicine, when referring to
human feces,
blood in stool looks different depending on (1) how early it enters the intestines (and thus how much digestive action it has been exposed to) and on (2) how much there is (a little bit, more than a little, or a lot). This is why bright red blood in the stool has different clinical significance (and a different name) than brown or black blood in the stool. Thus the term can refer either to
melena, with more blackish appearance, originating from
upper gastrointestinal bleeding, or to
hematochezia, with more red color, originating from
lower gastrointestinal bleeding. The term "blood in stool" is usually not used to describe
fecal occult blood, which refers to blood that is not visible and thus is found only after chemical testing is performed.