If bleeding occurs before the stool, the cause may be due to a lesion in the intestine. Depending on the location of the bleeding lesion in the intestine, it is divided into upper gastrointestinal bleeding and lower gastrointestinal bleeding, as follows: 1. If it is upper gastrointestinal bleeding, it is usually a manifestation of black stool, mainly caused by gastric ulcer, malignant tumor of the stomach, duodenal ulcer, and malignant tumor of the duodenum; 2. If it is lower gastrointestinal bleeding, it is often It is often caused by inflammation of the colon, polyps, or malignant tumors of the colon. If bleeding before stool is detected, it is recommended to choose different tests according to the type of bleeding in order to clarify the diagnosis. If the stool is black, gastroscopy is usually recommended to clarify the diagnosis, and if the stool is bright red blood, colonoscopy can be done to clarify the diagnosis.