The causes of dark red blood in the stool may be related to the following: a. acute and chronic gastritis, gastric ulcer, gastric cancer, etc., secondary to upper gastrointestinal bleeding, followed by dark red blood in the stool; b. acute and chronic enteritis, intestinal polyps, intestinal tuberculosis, colon cancer, etc., resulting in dark or red stools; c. in addition to primary gastrointestinal diseases, other diseases may also occur with dark or red stools. For example, haematological disorders (primary thrombocytopenic purpura, leukaemia, multiple myeloma, etc.), secondary to thrombocytopenia, can easily complicate gastrointestinal bleeding and result in dark clinical manifestations. In short, dark red blood in the stool is due to gastrointestinal bleeding.