Infections can occur during biopsies when too much tissue is removed and bacteria protrude in areas they do not belong to, or in cases when the lining of the colon is perforated and the bacteria get into the abdominal cavity. Infection may also be transmitted between patients if the colonoscope is not cleaned and sterilized properly between tests. Minor colonoscopy risks may include nausea, vomiting or allergies to the sedatives that are used. If medication is given intravenously, the vein may become irritated. Most localized irritations to the vein leave a tender lump lasting a number of days but going away eventually. The incidence of these complications is less than 1%. On rare occasions, intracolonic explosion may occur. A meticulous bowel preparation is the key to prevent this complication.Signs of complications include severe abdominal pain, fevers and chills, or rectal bleeding (more than half a cup or 100ml). Procedure
Preparation
The colon must be free of solid matter for the test to be performed properly. For one to three days, the patient is required to follow a low fiber or clear-liquid-only diet. Examples of clear fluids are apple juice, chicken and/or beef broth or bouillon, lemon-lime soda, lemonade, sports drink, and water. It is important that the patient remains hydrated. Sports drinks contain electrolytes which are depleted during the purging of the bowel. Drinks containing fiber such as prune and orange juice  should not be consumed, nor should liquids dyed red, purple, orange, or sometimes brown; however, cola is allowed.
Virtual colonoscopy does not allow therapeutic maneuvers such as polyp and tumour removal or biopsy, nor visualization of lesions smaller than five millimeters; if a growth or polyp is detected using CT colonography, it would require removal during a standard colonoscopy. Surgeons have used the term pouchoscopy to refer to a colonoscopy of the ileo-anal pouch. Medical uses
Conditions that call for colonoscopies include gastrointestinal hemorrhage, unexplained changes in bowel habit and suspicion of malignancy. Colonoscopies are often used to diagnose colon polyp and colon cancer, but are also frequently used to diagnose inflammatory bowel disease. In older patients (sometimes even younger ones) an unexplained drop in hematocrit (one sign of anemia) is an indication that calls for a colonoscopy, usually along with an esophagogastroduodenoscopy (EGD), even if no obvious blood has been seen in the stool (feces).Fecal occult blood is a quick test which can be done to test for microscopic traces of blood in the stool. A positive test is almost always an indication to do a colonoscopy. In most cases the positive result is just due to hemorrhoids; however, it can also be due to diverticulosis, inflammatory bowel disease (Crohns disease, ulcerative colitis), colon cancer, or polyps. Colonic polypectomy has become a routine part of colonoscopy, allowing quick and simple removal of polyps during the procedure, without invasive surgery. Colon cancer screening
Colonoscopy is one of the colorectal cancer screening tests available to people in the US who are 45 years of age and older.