Blood in the stool is defined as bleeding from the digestive tract, with blood being expelled from the body through the anus. The blood excreted can be bright red, dark red or black. A small amount of bleeding does not cause a change in stool color and requires an occult (occult) blood test to be determined, called occult blood. One of the purposes of clinical stool routine checks is to detect patients with occult blood. The bleeding may occur in the following ways: blood dripping from the anus during or after defecation, blood spraying, blood on the surface of the stool, blood staining of the hand paper after defecation, etc. Sometimes blood is mixed with stool, pus and mucus. However, the most common is blood in the stool or blood dripping from the stool, and the amount of blood may be more or less. The color of blood in the stool depends first of all on the height of the bleeding site. The upper gastrointestinal tract such as the esophagus, stomach and duodenum, as well as the liver, biliary tract and pancreas, bleed mostly in brown or tarry stools. The lower gastrointestinal tract, such as the small intestine, colon, rectum, and anal canal, bleeds mostly in dark red or bright red stools. However, the color of the blood stool is also related to the amount of bleeding and the speed of discharge. When acute upper gastrointestinal hemorrhage is accompanied by increased intestinal peristalsis, bright red blood stool can be excreted instead of black, while small intestine bleeding, if it stays in the intestine for a long time, can also excrete tar-like black stool. The most common causes of blood in the stool are: hemorrhoids: folklore has “nine hemorrhoids out of ten”, especially older men suffer from hemorrhoids more commonly. The painless intermittent blood after the stool is a common symptom of early internal hemorrhoids, because the stool rubs the mucous membrane of the hemorrhoid, there is blood dripping from the stool or blood on the stool paper, and a few of them bleed in the form of jets, which can stop on their own. Colon polyp: its blood in stool is similar to hemorrhoid, mostly intermittent and less bleeding. Colonic polyps have the possibility of cancer, so they should not be ignored. Anal fissure: It can also have fresh blood in the stool. A small amount of blood is often seen on the surface of stool or on the stool paper during defecation, or drops of fresh blood, but anal fissures mostly have the typical manifestations of pain around the anus, constipation and bleeding, and the pain is more intense and periodic. Colorectal cancer: In the world, colorectal cancer is the 4th most common malignant tumor. 2002, there were about 1 million cases of colorectal cancer and 530,000 deaths worldwide. In recent 20 years, the incidence rate of colorectal cancer in China has been on the rise. According to the survey results in 2004, the incidence rate of colorectal cancer has risen to the second or third place of gastrointestinal tumors in major cities such as Beijing and Shanghai in China. According to statistics, more than 70% of colorectal cancer patients have blood in stool, which is manifested as dark red blood in stool, or mucus-purulent stool, or blood mixed with stool. Adults who have blood in stool, accompanied by lower abdominal cramps or anemia and weight loss should be alerted to colorectal cancer. According to the analysis of relevant data, more than half of colorectal cancers in China are located in the rectum, the length of the rectum is about 15 cm, and 65% to 75% of rectal cancers occur in the lower 2/3 part, which can be detected in time by simple “anal finger examination”. In addition, it is worth noting that rectal cancer may coexist with hemorrhoids, so sufficient attention should be paid to blood in the stool, and in order to detect colon and rectal cancer in time, “anal finger examination” should be performed, and if necessary, sigmoidoscopy or fiberoptic colonoscopy should be performed for the whole colon. However, unfortunately, at present, 50% of patients who are not diagnosed in time due to rectal cancer with blood in stool are delayed for half a year, 70% of patients are delayed for 3 months, and only less than 10% of patients are diagnosed and treated in time. Rectal cancer is divided into early, middle and late stages, and the survival rate of early stage patients can reach 90% to 100%, middle stage patients can reach 40% to 60%, and late stage patients can only be below 20% after treatment. Therefore, early detection, early diagnosis and early treatment of rectal cancer are very important. Ulcerative colitis: Ulcerative colitis often causes chronic diarrhea, with 2 to 4 or more stools per day, mucopurulent stools, accompanied by abdominal pain and fever. A definitive diagnosis can be made by fiberoptic colonoscopy. The incidence of colorectal cancer in patients with ulcerative colitis is 5 to 10 times higher than that of the normal population, and the degree of malignancy is high, so early diagnosis and early treatment are also required. In addition, food poisoning, bacillary dysentery, amoebic dysentery, blood disorders, vitamin C and K deficiency, epidemic hemorrhagic fever, allergic purpura, and pediatric intussusception can also cause blood in the stool. In conclusion, blood in the stool is often a sign of many diseases, including diseases of the digestive system and other systems of the body can lead to blood in the stool, and a significant number of people with blood in the stool are patients with colorectal cancer, which is extremely harmful to people, so for any form of blood in the stool, you should seek early medical attention, perhaps a simple “one finger” (anal finger examination) can be a clear diagnosis, and early surgery can save valuable lives. Early surgical treatment can save precious lives.