Blood in stool

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.

In infants, the Apt test can be used to distinguish fetal hemoglobin from maternal blood.