Bleeding from upper intestine ,most commonly from an ulcer in stomach and duodenum causes black stool .Black stool is due to action of acid (hydrochloric)on the hemoglobin (present in the red blood cells).That is substantiated by occult blood test of a stool sample.
The exact disease of stomach and duodenum can be determined by endoscopy.Amongst various other causes of bleeding cancer of stomach, esophageal varices and tear of upper end of stomach are important.
Bleeding blood vessels in an ulcer can be sealed endoscopically and further blood loss be prevented. Along with that acid suppression also important.Some times it may be required to transfuse blood to the patient.
Analgesics are most common triggering factor for ulceration and subsequent bleeding.To prevent this dreaded complication analgesics to be taken when it is essential and informing doctor for previous acid peptic disease while getting treatment is absolutely necessary.