Colonoscopy before the bowel cleansing pulled out the slag with blood, may be with the bowel cleansing stimulation, ulcerative colitis, rectal polyps and other factors, it is recommended to combine with the results of the colonoscopy, give observation, drug treatment, surgical treatment and so on. 1. Irritation of purging: Because the purging laxative itself has a certain degree of irritation, and the mucous membrane of the rectum is more sensitive, so a small amount of blood can be discharged when stimulated, which is a normal phenomenon. Observation can be given, generally can recover on their own. 2. Ulcerative colitis: the etiology is unknown, the typical symptom is that the patient discharges mucus, pus and blood. Therefore, bowel clearing before colonoscopy can be pulled out with blood in the stool, often accompanied by abdominal pain, diarrhea, anxiousness and heaviness (lower abdomen is uncomfortable, want to relieve the stool, after defecation, there is a sense of incomplete) and other symptoms. After diagnosis, you can follow the doctor’s instructions to use salicylazosulfapyridine, prednisone and other drugs. 3. Rectal polyps: often associated with family genetic factors, inflammation and other chronic stimuli, patients can discharge mucus blood stools, often accompanied by a sense of urgency and heaviness (discomfort in the lower abdomen, wanting to defecate, and a sense of incomplete defecation after defecation). It can be removed endoscopically. Generally patients should avoid spicy, stimulating, indigestible and too greasy food for a period of time before the colonoscopy. There may be other reasons for the blood in the sludge pulled out from the bowel before colonoscopy, so you should consult a professional physician in time, according to the results of the colonoscopy, and follow the doctor’s instructions to carry out standardized treatment.