What causes a little blood ON stool as opposed to blood IN stool? I've had a little bright red blood ON stool prev, but negative FOBT in Dr office.

Blood coating stool. Blood coating stool but negative occult blood is most likely do to minor hemorrhoidal bleeding. if it is frequent, I would recommend a rectal exam and proctoscopy. If it is rare that would not be necessary . If wish a therapy please ask for a consult and I will advise a treatment.