In the last article, we concluded that most average-risk individuals should start getting screened for colorectal cancer at age 50, and that colonoscopy is the best available screening test. That part was easy! In this article, we will tackle a much more challenging and controversial question: How often do you need to repeat a negative colonoscopy?
Let’s start by reviewing what the guidelines recommend. For an average-risk individual (no significant family history of colon cancer, no symptoms, and no polyps found on prior colonoscopy), the published guidelines are as follows:
- The American College of Gastroenterology recommends repeating a colonoscopy every 10 years.
- The US Preventive Services Task Force recommends repeating a colonoscopy every 10 years.
- The American Cancer Society recommends repeating a colonoscopy every 10 years.
Clearly, the screening guidelines recommend repeating a negative colonoscopy in ten years. Now what if I told you that many (if not most) practicing gastroenterologists recommend repeating the test in five years, not ten? Are there situations where this is appropriate? Why do so many doctors recommend repeating the exam in 5 years?
In my mind, the biggest hesitancy that gastroenterologists have in sticking to the 10 year screening guideline is the fear of an interval cancer occurring. An interval cancer is one that develops within the proper screening interval. We know that it typically takes about 10-15 years for a small polyp to grow and transform into colon cancer. However, it is now known that certain subtypes of polyps may make the change from benign to malignant faster than 10 years. Furthermore, there is also a growing appreciation that flat right-sided polyps are not always easily detected on colonoscopy and therefore can be missed. Perhaps even more worrisome is the fact that although colonoscopy is the best test for preventing colon cancer, it is not perfect: There is a significant “miss rate” of small polyps in even the most expert of hands. All of these issues can lead to interval cancer development.
Perhaps a bigger issue is the fact that guidelines apply to populations, and doctors don’t treat populations, they treat individual patients! Guidelines are not laws, they are merely a framework to use when taking care of most patients. I’m not a big fan of emotional reasoning when it comes to medical data, however many individual patients are worried about getting cancer and ask for screening around 5-8 years from their last exam. I can reassure them that waiting 10 years is perfectly safe by using cold guidelines printed in a journal, but it’s often a difficult and uphill battle when my patient says, “Please, I just want you to check me out now doc.”
Remember that the guidelines also aim to limit unnecessary colonoscopies for the population as a whole by accepting the necessary fact that some interval cancers will occur. It’s just a matter of where you set the acceptable miss rate: For example, if colonoscopies were repeated every 9 years instead of 10, there will be more cancers and polyps caught at the expense of ~10% more colonoscopies being done. I can guarantee that the patient who was “saved” by a colonoscopy done earlier than 10 years doesn’t really care about those extra colonoscopies, however the patient that had a complication from an unnecessary colonoscopy probably feels very differently!
I’d also like to bring up the issue of the patient who had a colonoscopy by a different doctor, and who now comes to see me to arrange the next one. This happens more than you’d think, as people move, or their primary doctor refers them to someone different, or simply due to patient preference. Even with the prior negative colonoscopy report in hand, can I confidently give that patient a 10 year screening interval? What was that other doctor’s adenoma detection rate? Did they mention the quality of the bowel prep? Did they use proper scope withdrawal technique for the minimum amount of time needed to perform a high-quality inspection? The truth is that this situation makes it impossible for me to confidently give that patient a 10 year screening interval because of all these unknowns, so I usually recommend repeating the test in 5 years.
Alright, I admit it; I left out the most important part. This article could not be complete without mentioning reimbursement as one of the reasons why many doctors repeat colonoscopies earlier than the 10 year recommended interval. It is true that the current fee-for-service financial model of medicine rewards all doctors for doing more of everything, but this is slowly changing to a performance-based system. Furthermore, I would argue that gastroenterologists could make a comparable amount of money and help prevent and diagnose many more colon cancers by screening a larger population of people at 10 year intervals, rather than a smaller group of patients at 5 year intervals. The sad fact is that only about 65 percent of the 50-75 year-old population is up-to-date with any form of colorectal screening (with only 40% of the general population having a screening colonoscopy as recommended), so fear not my GI colleagues, there are still plenty of patients out there to scope!
So with all of that being said, how can we confidently recommend a 10 year follow up interval for screening colonoscopy? In one word, the answer is quality. A high-quality colonoscopy: 1) is performed by an expert endoscopist with a high adenoma detection rate, proper inspection technique, and adequate withdrawal time; 2) is done using a modern high-definition scope, and; 3) requires that the patient have either good or excellent bowel prep. If you are providing high-quality colonoscopy, then you should stick to the 10 year interval that the guidelines recommend.
What do I do? For average-risk nonsmoking nonobese patients in whom I have performed a negative high-quality screening colonoscopy, I follow the guidelines and recommend the next screening colonoscopy in 10 years. For patients outside of this category, it is an individualized choice, but often boils down to me recommending a 5 year interval.
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Rex DK, Johnson DA, Anderson JC, et al. American College of Gastroenterology guidelines for colorectal cancer screening 2008. Am J Gastroenterol 2009;104:739-50.