Questions and Answers about Quality in Colonoscopy

1. Why is quality important in colonoscopy?

Although colonoscopy has been available in clinical practice for more than 40 years, only in the past 15 years has awareness developed that the success of colonoscopy in preventing colorectal cancer and minimizing complications is very dependent on the skill and competence of the colonoscopist. Colonoscopists differ substantially in the number of precancerous polyps they detect during colonoscopy and in how often they perform colonoscopy in response to both normal and abnormal findings. Awareness of these differences led the U.S. Multisociety Task Force on Colorectal Cancer in 2002, as well as a joint task force of experts from the American College of Gastroenterology and American Society of Gastrointestinal Endoscopy in 2006, to propose quality indicators that colonoscopists can use to measure how effectively and safely they perform colonoscopy. Obviously, patients have an interest in undergoing the most effective and safe colonoscopy possible, and achieving these goals requires a colonoscopist who is committed to high quality.

2. Does the quality of examination differ among colonoscopists from different specialties?

Studies have shown average performance of colonoscopy by gastroenterologists to be superior to that of primary care physicians in three different areas of colonoscopy performance. First, three population-based studies have found that gastroenterologists performing colonoscopy are less likely to miss colorectal cancer than are primary care physicians who perform colonoscopy. This may reflect the more extensive training that gastroenterologists receive in this procedure and their higher volumes of colonoscopy in practice. Second, gastroenterologists’ patients are less likely to incur serious complications during colonoscopy, such as perforation or making a hole in the colon, compared to primary care physicians. Third, gastroenterologists are less likely than both primary care physicians and general surgeons to perform colonoscopy at intervals that are considered too short according to current guidelines. Whether this difference reflects a lack of confidence among primary care physicians and general surgeons in the quality of their colonoscopy or lack of awareness of current guidelines is unknown.

3. Is there variation in quality of performance among members of the same specialty?

Even though gastroenterologists have on average the highest level of training and their examinations have been shown on average to be superior to primary care physicians, there is considerable variation among gastroenterologists in their detection rates of precancerous polyps. Therefore, it is essential that every colonoscopist, regardless of specialty, makes measurements to establish that their examinations are effective. It is very reasonable and appropriate for patients to ask questions of their colonoscopist about whether quality measurements are being made and their results.

4. How can I be sure that I will receive a careful examination of my colon?

The measurement that best reflects how carefully colonoscopy is performed is a doctor’s "adenoma detection rate." This rate is defined as the percentage of patients age 50 and older undergoing screening colonoscopy, who have one or more precancerous polyps detected. This rate should be at least 25% in men and 15% in women. A secondary measure of careful examination is that doctors should have an average withdrawal time of at least six minutes. The withdrawal time is the time it takes to remove the scope from the colon. This interval is important because this is the phase of colonoscopy when most doctors actually examine the colon systematically for polyps. It is perfectly reasonable to expect doctors to have measured their adenoma detection rate and to record their withdrawal time. It is also reasonable to ask for a copy of the colonoscopy report that documents that the colonoscope was advanced to the very beginning of the colon and that the landmarks of that portion of the colon (called the "cecum") have been documented by notation in the report and by photography.

5. Why is bowel preparation for colonoscopy important, and what can I do to make sure my colon is thoroughly cleansed for the procedure?

Colonoscopy is a video examination of the colon. The video camera and the colonoscope, like any other video camera, cannot see through solids. Therefore, the colon must be thoroughly cleansed to provide the doctor the best opportunity possible for a thorough and detailed examination.Be sure to pick up and read your written bowel preparation instructions at least several days before your colonoscopy. Go over the instructions and make sure you have all of the materials needed to complete the preparation.The most effective bowel preparations involve "split" dosing of the laxatives, in which half of the preparation is taken on the morning of the examination, usually 4 to 5 hours before the time of the scheduled colonoscopy, and completed at least 2 to 3 hours before that time. If you are scheduled at 7 or 8 in the morning, this will mean getting up very early to take the second half of the preparation. If the instructions call for split dosing, do not alter the timing of the doses. It is worth the inconvenience of getting up in the middle of the night to make sure that you have a very effective preparation. The timing of the second dose in relationship to the colonoscopy is critical. If too long an interval is allowed between the end of the second half of the preparation and the timing of the colonoscopy, mucus and secretions will come out of the small intestine and stick to the cecum and right colon.


To ensure an effective and safe colonoscopic examination, find a well-trained colonoscopist who is committed to making quality measurements. It is fair to ask the colonoscopist to be sure to do a slow and careful examination and to provide a copy of the report that documents and photographs the complete extent of examination. Take the bowel preparation instructions seriously. Pick up the written instructions early, read them early, and follow them carefully. When colonoscopy is done carefully and with an effective preparation, it is a very powerful cancer prevention technique.