A. Blood coming from the upper gastrointestinal tract, with tarry or black stools accompanied by unexplained anemia, emaciation or upper abdominal masses, is mostly stomach cancer bleeding; accompanied by plain acid reflux, belching or nighttime pain, hunger pain, indicating the possibility of bleeding from stomach and duodenal ulcers; if there is a history of liver disease or schistosomiasis, it may be esophageal bleeding from liver cirrhosis. However, when the upper gastrointestinal bleeding is large, the stool can also be bright red or dark red, when it is often combined with vomiting blood. Once there is upper gastrointestinal bleeding, especially if there is heavy bleeding, you should go to the hospital promptly and receive a gastroscopy to clarify the diagnosis. Second, the blood coming from the lower gastrointestinal tract, the stool is blood-colored red. 1, hemorrhoids: hemorrhoids is the most common cause of blood in the stool, bleeding occurs mostly in the process of defecation, bright red blood, attached to the surface of the stool; can also be after the stool, in the form of drops and drops or jets out, bleeding can be small only in the hand paper to see fresh blood. In the force of defecation, there can be a small lump from the anus out. 2.Anal fissure: The blood in the stool caused by anal fissure is bright red, often occurs after constipation, the bleeding volume is small, manifested as blood dripping from the anus after stool or blood on the hand paper, accompanied by severe pain in the anus during defecation, the pain is slightly relieved after stool, and then starts to be severe again. 3.Colorectal cancer: 85% of early rectal cancer only manifests as blood in stool, and more than 90% of rectal cancer cases are misdiagnosed as hemorrhoids in the early stage, among which 1% to 3% are finally diagnosed as rectal cancer. The blood in stool caused by rectal cancer is most similar to hemorrhoid bleeding, but most of it is mixed with mucus and dark blood clots in the blood or stool, and accompanied by anal drop, deformation of stool, thinning, increasing frequency or incomplete defecation; colon cancer often has changes in stool habits, including constipation, diarrhea or both alternately, followed by abdominal pain, abdominal discomfort or abdominal masses, and in the late stage, anemia and emaciation may appear. 4, rectal polyps: rectal polyps caused by blood in the stool is bright red, painless, blood and stool do not mix. 5, colitis, proctitis: most of the blood in the stool mixed with mucus and pus-blood stool, accompanied by abdominal pain, fever, increased frequency of defecation and incomplete defecation. Third, systemic diseases, accompanied by systemic bleeding blood in the stool with bleeding from the skin, mucous membranes or other organs, mostly seen in blood system diseases and other systemic diseases, such as leukemia, hemophilia, uremia and some rare infectious diseases.