Blood in the stool and vague pain in the left lower abdomen are common in the following conditions: the first condition, hemorrhoids, hemorrhoids blood in the stool is often blood in the stool or bleeding after the stool, mainly fresh blood stool. The second condition, ulcerative colitis, is often pus and blood in the stool with abdominal pain and other symptoms, and can have the symptoms of wasting if the disease is prolonged. In the third case, cancer, tumors of the intestinal tract may also cause blood in the stool, and may be accompanied by changes in bowel habits or thickness. Of course, the above is only a preliminary diagnosis from the symptoms, and further examination and laboratory tests should be done to confirm the diagnosis.