Black, tarry stools
Bleeding in the gastrointestinal (gi, gut) tract can be unnoticed if low amounts and intermittent.
Lower GI bleeds can result in bright red blood per rectum (brbpr) or maroon stools
. Bleeding in the upper GI tract passes through the bowels and gets transformed to a black tarry, or sometimes called "coffee grounds" look. A simple test for blood is the fecal (stool) occult blood test.