Frequently Asked Questions About Colonoscopies

How can I determine if I received a thorough colonoscopy?

A colonoscopy is an exam in which a thin, flexible, lighted viewing tube (a colonoscope) is threaded up through the rectum for the purpose of inspecting the entire colon (large intestine/bowel) and rectum to detect changes or abnormalities.

Question I just turned 50 and had my first screening colonoscopy.  My gastroenterologist advised me to have a follow-up exam in 10 years since he didn’t find any polyps.  How do I know that I received a thorough exam and can safely wait 10 years?

You have made a very important decision to proceed with colon cancer screening.  Colon cancer is the second leading cause of cancer deaths in America with an estimated 55,000 persons dying per year.  Colonoscopy is currently our most effective means of reducing the incidence of colon cancer with reductions in some studies of up to 80–90%.  Despite this remarkable reduction only slightly over one-third of eligible persons elect to have a colonoscopy.  With the inconvenience and expense of colonoscopy incurred, one should expect and receive a thorough examination that provides a sense of security until the follow-up screening exam is performed.  In your case, without a noted family history of colon cancer, the appropriate time interval for the second exam would be the recommended 10 years.


An endoscope is a thin, flexible tube with a light and a lens on the end used to look into the esophagus, stomach, duodenum, small intestine, colon, or rectum. The procedure that uses an endoscope is called an endoscopy. There are many types of endoscopy; colonoscopy is one type.

Your concern about receiving an adequate exam that will provide you reassurance for the next decade is justified.  I will briefly present some information that may be of assistance in choosing an endoscopist that can perform a colonoscopy exam that minimizes missed lesions.Assuming you have chosen a physician who is board certified (who has completed specialty training and passed an examination earning certification of proficiency from an independent board), and has completed supervised training in endoscopy, it first needs to be noted that even in the best hands there is an inherent miss rate when performing colonoscopy.  The miss rate varies depending on the size of polyps one is reviewing.  The larger the polyp the less likely it is to be missed.  With polyps larger than 1cm (0.4 inch) the miss rate can be as high as 6% – higher with smaller polyps.A number of recent studies have been conducted to look at the disparity in miss rates among different physicians performing endoscopies.  Withdrawal times – the time it takes to remove the endoscope from the colon – was found to be a significant factor in polyp detection rates.  Physicians having a withdrawal time of less than 6 minutes found significantly fewer polyps.  These studies suggest that a longer exam may lead to a more careful inspection of the colonic mucosa resulting in fewer missed polyps.  It is very reasonable to ask your endoscopist what his or her withdrawal times are.

Advancing the endoscope to the beginning of the colon (cecum) and performing a careful visual inspection of this area is crucial in the prevention of missed lesions.  The cecum is the area of the colon that connects to the small intestine.  During endoscopy this area can be identified by the doctor.  Photo documentation of the cecum should be the norm in all endoscopic practices.  A quality endoscopist should be able to reach the cecum in 95% of screening colonoscopies.  How often (percentage of times) your endoscopist reaches the cecum is another means of measuring quality endoscopy.

An additional measuring tool for quality endoscopy is the adenoma detection rate.  Adenomas are a type of colon polyp that can develop into cancer over time.  The key benefit of screening colonoscopy is to remove these premalignant lesions.  In the average risk male patient undergoing screening, a detection rate of roughly 25% should be expected.  For women the expected rate of detection is about 15%.  If an endoscopist has a detection rate significantly less than these bench marks, a concern regarding missed polyps would need to be entertained. Ask the endoscopist what his or her average detection rate is of adenomas.

In gastroenterology the specialty societies (American College of Gastroenterology, American Society of Gastrointestinal Endoscopy, American Gastroenterological Association) have taken the lead in performing research to identify quality measurements which can be used to assure patients are receiving a thorough endoscopic exam.  Polyp detection rates, cecal intubation rates, and withdrawal times are measurements that physicians performing endoscopies should know for the benefit of their patients.

– Thomas Puetz, MD

Can having a colonoscopy cause a change in bowel habit?

Eight months ago I had a screening colonoscopy that came back normal. Up to that point I was a physically very fit and healthy male in my 70’s. But after the colonoscopy I immediately began experiencing severe constipation. I had never had this before. My doctor prescribed a fiber supplement which did not help. He also performed an MRI which came back negative. No one knows what is wrong or how to treat this. My life has changed dramatically since this has happened and I am no longer able to function normally. For all practical purposes this has made me a prisoner in my home. What could have caused this change during a colonoscopy?
There is no straight-forward answer to this question. In my practice I see mostly patients with functional GI disorders and I have observed that it is not that uncommon for patients with irritable bowel syndrome (IBS) to say that colonoscopy seems to upset their condition.  Fortunately, this is usually only short term but occasionally some patients can continue suffering for a considerable period of time.  The cause of this problem is uncertain, but in my experience it is not due to incompetence on the part of the colonoscopist.
My particular view is it could be something to do with the preparation for the colonoscopy, which usually involves the use of a strong laxative.  We have shown in my laboratory that the administration of a laxative can sensitize the bowel, even in people without IBS, so one could imagine that it could cause even more of a problem in someone whose bowel is already sensitive as is the case in IBS.  On the other hand, many IBS patients with constipation as their predominant bowel symptom can only function if they are taking a laxative on a regular basis.
Obviously it would be nice if one could prevent this problem, but at the present time there is no way of predicting who will and who will not react badly to a colonoscopy.  For persons with IBS it may be worth considering being rather cautious with laxatives when diarrhea is the predominant bowel symptom and it would their doctor to know if they ever had a tendency to diarrhea before the examination.  Finally, it is important to remember that the gut can take months rather than weeks to recover from any form of insult, and so there is still plenty of time for you to get better.– Peter Whorwell, MD

Learn more about motility testing


Adapted from “How Can I Determine If I Received a Thorough Colonoscopy?”-IFFGD Publication #232 by Thomas Puetz, MD, Aurora Advanced Healthcare, Mequon, WI, published in Digestive Health Matters, Vol. 16, No. 2, and an article published in Digestive Health Matters, Vol. 17, No. 1, by Peter Whorwell, MD, Professor of Medicine and Gastroenterology, University of Manchester, United Kingdom.

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