The signs of bleeding in the digestive tract depend upon the site and severity of bleeding. If blood is coming from the rectum or the lower colon, bright red blood will coat or mix with the stool. The stool may be mixed with darker blood if the bleeding is higher up in the colon or at the far end of the small intestine. When there is bleeding in the esophagus, stomach, or duodenum, the stool is usually black or tarry. Vomited material may be bright red or have a coffee-grounds appearance when one is bleeding from those sites. If bleeding is occult, the patient might not notice any changes in stool color.

If sudden massive bleeding occurs, a person may feel weak, dizzy, faint, short of breath, or have crampy abdominal pain or diarrhea. Shock may occur, with a rapid pulse, drop in blood pressure, and difficulty in producing urine. The patient may become very pale. If bleeding is slow and occurs over a long period of time, a gradual onset of fatigue, lethargy, shortness of breath, and pallor from the anemia will result. Anemia is a condition in which the blood's iron-rich substance, hemoglobin, is diminished.