Not necessarily, most cases of tarry stools are caused by bleeding in the upper gastrointestinal tract. However, there are a few patients who have a small to moderate amount of bleeding from the lower gastrointestinal tract and the stool stays in the intestine for a longer period of time before being expelled, giving the stool a tarry colour.
In addition, certain special conditions, such as bleeding from the mouth after the nose or blood being swallowed during hemoptysis in the lungs, can also result in tarry stools.