The causes of blood in stool in leukemia patients are considered to be related to thrombocytopenia, coagulation dysfunction and perianal disease. 1. Thrombocytopenia: the number of platelets in leukemia patients can be normal or mildly reduced in the early stage, and can be significantly reduced in the middle and late stages. Platelets play a role in stopping bleeding in the body, and the decrease in the number of platelets can easily lead to bleeding conditions, such as blood in stool, skin ecchymosis, hematuria and so on. 2. Coagulation dysfunction: leukemia, especially acute promyelocytic leukemia, can have abnormal coagulation function in the early stage, with a large release of procoagulant substances and consumption of coagulation factors, thus the body is in the state of bleeding, with extensive and serious bleeding, such as ecchymosis of the skin, blood in the stool, hematuria, and so on. 3. Perianal diseases: If leukemia patients themselves suffer from hemorrhoids, anal fistula, anal fissure and other diseases, blood in stool will also occur. The blood in the stool is often bright red, with blood on the stool paper or dripping blood. Leukemia blood in stool may have other causes, such as rectal tumors, inflammatory bowel disease, dysentery, etc. It is recommended to go to the hospital in a timely manner to improve the examination and clarify the cause of the disease.