gastroenterologist doctors wellington

How do I know if I am getting a quality colonoscopy?

A good quality colonoscopy can give reassurance about your risk of bowel cancer for years or even decades. A good quality colonoscopy results from a combination of cleaning your bowel out well beforehand, and having a skilled colonoscopist performing the procedure. The skill levels of colonoscopists vary, and finding a good one may involve asking questions about performance measures as discussed below.

In the decades since it was first developed, colonoscopy has changed from being a test used simply to look for cancers or large polyps which would then be removed by a surgical operation, to one that can prevent cancer by removing the polyps during colonoscopy and that gives a good idea about your future risk of cancer. For this reason, the skill level required to be an quality colonoscopist has greatly increased.

There are medical studies that show a normal colonoscopy in those aged over 50 predicts for a significantly lower than average risk of bowel cancer for 20 years, and even if a significant polyp is removed during a colonoscopy, the risk of bowel cancer remains low for at least five years. This is reliant, however, on the colonoscopy having been of good quality, and the colonoscopist not having missed other significant polyps during the examination. A quality colonoscopy gives excellent prognostic information about future cancer risk, and allows maximisation of the time interval between colonoscopies without the risk of cancer development because a significant polyp was missed. So how can you guarantee you receive a quality colonoscopy?

An adequately cleansed bowel is critical to ensure that residual faecal material does not obscure the identification of important findings, especially polyps. As such, being very particular in taking the bowel preparation purgative solution (Glycoprep, Picoprep etc) exactly as described by the nursing staff is very important.

However, much as with any skill-based task such as building or carpentry, the major determinant of the quality of a colonoscopy is the ability and the technique of the operator. The operator must view as close to 100% of the bowel surface as possible, and must be able to remove safely any polyps found. This requires searching carefully behind all the colonic folds, being aware of and paying special attention to visual blind spots in the colon, being alert to flat polyps that may be very inconspicuous, and having an efficient and effective polypectomy (polyp removal) technique. These skills are training-dependent, and currently vary widely amongst operators in NZ. So how can you tell if your colonoscopist provides a quality product?  Do not assume your GP knows this information about the colonoscopist(s) he or she refers you to.

Most endoscopy units in NZ are now required to audit the practice of the colonoscopists that work in them. The data collected encompasses three important area of quality: efficacy, patient comfort, and complications. Your colonoscopist should be able to confirm that he or she is part of a continuous audit programme and quote his or her performance in these three areas.


Caecal intubation rate – the percentage of colonoscopies that the colonoscopist passes the colonoscope as far as the caecum, the farthest point of the colon. Someone who does not perform well here commits patients to either repeat colonoscopies, or another test called CT colonography, or risks missing polyps that were beyond the point that the colonoscope was passed to. A moderately skilled operator should achieve a caecal intubation rate of greater than 95%, but the more able colonoscopists should have rates of >98%.

Adenoma detection rate – the percentage of colonoscopies in which a potentially significant type of polyp, an adenoma, is detected (this is different from ‘polyp detection rate’ which may include insignificant hyperplastic polyps). In the average NZ population receiving colonoscopies, this percentage should be at least 30%. If a colonoscopist has a low adenoma detection rate then it implies that he or she may not be an effective searcher, and therefore may miss significant polyps more often, which reduces the prognostic value of his or her colonoscopies, and increases the risk of ‘interval cancers’ – bowel cancers occurring within 3-5 years after a colonoscopy.

Withdrawal time – the amount of time spent by the colonoscopist searching the colon as the colonoscope is withdrawn from the caecum. This is the part of the examination where most polyps are found, so a colonoscopist who pulls the colonoscope out rapidly is less likely to have performed an adequate exam. The optimum withdrawal time is considered to be 6-10 minutes.

Patient comfort

Colonoscopy in most patients should not be an unpleasant experience.

If a colonoscopist causes excessive discomfort during a large percentage of colonoscopies, or needs to administer large amounts of sedative medication in a large percentage of colonoscopies, then his or her technique is likely to be poor. This may carry over into poor performance in efficacy measures, and deters patients from having repeat procedures. Those patients may also tell friends or relatives about the terrible experience, putting them off having bowel symptoms investigated.

A quality colonoscopist will have a high percentage of patients experience no or minimal discomfort during colonoscopies, and should use little sedative medication in most patients.


The most common 'complication' that can occur in colonoscopy is the colonoscopist not seeing and therefore not removing a large polyp which then might grow into a cancer.  The risk of a large polyp being missed is thought to be somewhere between 2 and 6%, with the risk of a cancer developing within a few years of a colonoscopy about 1 in 1000.  This risk might be higher with some colonoscopists, and lower with those with better technique.  It is known that the risk of missing polyps increases the longer a session goes on, probably because the colonoscopist gets tired and less attentive, so try and avoid being the last person on a colonoscopy list!  It is generally thought that a colonoscopist should not be performing more than 5-6 colonoscopies in a session.

For basic colonoscopies where only small polyps are removed, or just biopsies are taken, complications such as bowel perforation (making a hole in the bowel wall), significant bleeding, or sedative problems should be exceptionally rare.

In therapeutic colonoscopies, where very large polyps are removed, or strictures (narrowings) are dilated (stretched up with a balloon), then complication rates are always going to be much higher. If you are having a therapeutic colonoscopy it is very important to discuss in detail with your colonoscopist the likelihood of complications, what is the plan if a complication occurs, and how the risk of complications compares with either doing nothing or having surgery instead.