My Colonoscopy & My Thoughts on Colonoscopy Guidelines

Steven Kornweiss, MD cancer screening, colorectal cancer 1 Comment

Summary First

  • My post-colonoscopy video
  • Colorectal cancer screening guidelines
  • The basis for the guidelines
  • Where the guidelines fall short
  • Quantifying the risk of perforation with colonoscopy
  • How to get the best possible colonoscopy
  • Questions you can ask your gastroenterologist
  • My colonoscopy experience


If you saw my "post-op" video on social media (Instagram or Facebook), you already know I had a colonoscopy this week. If you’re wondering why I had this done at age 36, it was actually because I had a few concerning symptoms. Thankfully, I received a clean bill of health. However, had I not had symptoms, I still would have opted for a screening colonoscopy in four years from now when I’ll turn 40.

The Guidelines

Typical screening colonoscopy or fecal screening tests for colorectal cancer are now recommended at age 45, but more commonly, people have their first colonoscopy or screening test at age 50.

For some people, this is too late. Although the overall incidence of colon cancer is going down, the incidence in younger people is going up.

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Source: American Cancer Society – Colorectal Cancer Facts & Figures 2020-2022

You can see in the chart above, while most colon cancer is diagnosed in individuals over the age of 45, there are plenty of cases below that age. During the period of 2012-2016, there were 10.5 cases of colorectal cancer for every 100,000 people between the ages of 35-39, and 19 per 100,000 for people between the ages of 40-44. For simplicity’s sake, if we assume uniform risk across the population, an individual’s risk of being diagnosed with colorectal cancer during this four year period was 1 in 9,500 for those 35-39 years of age, and roughly 1 in 5,000 for those between 40 and 44.

For some people who have a family history of early colon cancer, screening can start 10 years earlier than the age at which a family member was diagnosed. So, if a family member had colorectal cancer at age 40, screening might start as early as age 30.

Guidelines are optimized for groups, not individuals

Guidelines recommend colonoscopy once every 10 years if an adequate and normal colonoscopy is obtained. This recommendation is based on the following three ideas:

  1. Nearly all colon cancer starts as a non-cancerous adenomatous polyp which can be visualized, removed, and tested during colonoscopy.
  2. It takes roughly 10 years for an adenoma to become a carcinoma.
  3. Adequate colonoscopy does not miss polyps.

These are good assumptions. It’s estimated that only a few out of every thousand polyps can progress to cancer in less than ten years. The elapsed time between when a polyp first develops and when it becomes cancerous is called “polyp dwell time.” According to the “Colorectal Cancer Screening: Clinical Guidelines and Rationale” published by the American Gastroenterological Association” in 1997 stated:

“[An expert] panel estimated that it takes an average of about 10 years for an adenomatous polyp, particularly one less than 1 cm in diameter to transform into invasive cancer.”

However, the panel found that in some cases, it might be possible for polyp dwell time to be as short as 3-5 years.

In a case-cohort study by Chen et al. published in the British Journal of Cancer in 2003, a statistical model was used to predict that polyp dwell time for small adenomas (0.6-1cm) is 7.75 years and for large adenoma (greater than 1 cm) is 5.27 years. The study also predicted that as many as 30% of colon cancers can arise de novo, which means that they may arise without first starting as a benign polyp. This finding contradicts statements to the contrary which can be found in almost every guideline on colon cancer which usually state that colon cancer “almost always” starts as a benign polyp.

The miss rate of colonoscopy is also a question. This is somewhat user dependent, and also depends on the quality of your preparation.

Overall, if you estimate that some colon cancer arises de novo as opposed to starting as a benign polyp, and that some early cancers and polyps will be missed on colonoscopy, and that polyp dwell time could be as short as 5 years, then in some cases, a 10 year interval will not be frequent enough to detect polyps before they become cancerous or to detect early localized cancer before it becomes metastatic.

For this reason, if you are a person who wants to be as aggressive as possible with preventive care and to decrease your chances of developing colon cancer, you might choose to have colonoscopies earlier and more frequently than the guidelines recommend.

How can we improve our chances?

For many people, this is impractical. But, in lieu of earlier and more frequent colonoscopy, there are a few things we can do to improve the quality of the colonoscopies that we do get.

  1. Utilize the guidelines to your advantage. Patients at higher risk due to certain medical conditions, family history, or genetics may be able to obtain earlier and more frequent colonoscopy.
  2. Prepare your colon perfectly so the gastroenterologist performing your colonoscopy can have the best possible chance of visualizing any abnormalities.
  3. Choose the most skillful, thoughtful, and thorough doctor you can find to perform your colonoscopy.

The first and second of these are fairly straight forward, but the third, not so much. How can we choose the best GI doctor to perform our colonoscopy?

In an excellent newsletter on colorectal cancer screening from 2020, Peter Attia provided a list of questions you can ask your gastroenterologist in order to assess their endoscopy skills. He recommends asking at least these four questions:

  1. What is your adenoma detection rate?

    According to Dr. Attia’s newsletter, the benchmark is 30% in men and 20% in women.

  2. What is your perforation rate?

    A literature review by the USPSTF estimated perforation rate for screening colonoscopy to be roughly 1 in 2,500. However, in my review, I found rates as low as 1 in 10,000 for screening colonoscopy. In a study done at Baylor In 2015, out of 3,137 patients who underwent screening colonoscopy, there were 0 perforations.

  3. What is your withdrawal time?

    Withdrawal time is the time it takes the endoscopist to withdraw the scope from the ileum back out to the anus. According to Dr. Attia’s newsletter, and much of the gastroenterology medical literature, a 6-minute withdrawal time is considered standard. Some studies, including this study published in NEJM in 2006, suggest that an endoscopist who takes more time may have a higher adenoma detection rate, and thus a lower rate of false-negative colonoscopy.

  4. What is your cecal intubation rate?

    The cecum is the part of the bowel at the intersection of the small bowel and the colon. A good endoscopist should be able to navigate the entire colon all the way into the cecum. According to Dr. Attia’s newsletter, a good rate of cecal intubation is above 95%. In the NEJM study referenced above, cecal intubation rate was 97% or above for each of the 12 gastroenterologists included in the study. Three of the physicians achieved a rate of 100% within the study.

Practically speaking, it may be very hard to ask your doctor all of these questions and to fully understand their answers. And, depending on the answers you get, where you live, and who the alternative physicians are, you might have to settle for the most available physician.

For example, even though I’m a physician and I know lots of gastroenterologists who practice near me, I really had only one option for an expedient test. I would’ve waited months for another physician to have availability. If I was having a routine screening colonoscopy, and I thought far enough in advance, I might have been able to broaden my options, to make additional phone calls, ask more questions, and get additional recommendations.

If it’s possible to get your gastroenterologists’s colonoscopy statistics, that’s great, but I think most experienced gastroenterologists who come highly recommended by other discerning physicians will produce good results in a well-prepared patient.

My Colonoscopy

The last thing I’ll mention here is that colonoscopy can be scary. I know lots of people who won’t go because they’re afraid of the procedure itself, and of the results.

It’s unusual to imagine someone navigating your colon with a camera while you’re unconscious, but to a gastroenterologist, that’s just a regular day at the office. Unsolicited, my doctor told me, “I love doing colonoscopies.”

Tests can be scary, but this is a safe test, it’s done all the time, and we need to know the results. Knowing beats not knowing every time.

If it helps, here’s how mine went:

I fasted for the duration of the day prior to my colonoscopy, drinking only my prep and water. I used a prep called Suprep. It’s a liquid that comes in two 6 oz. bottles. You mix the Suprep with 10 oz. of water. It’s a solution of sodium, magnesium, and potassium sulfate, sucralose, flavoring, and citric acid. It’s sort of like a sports drink, but 10x the salt and syrup factor. I drank the first dose around 1pm. Roughly 20 minutes later, this ran its course. At 930pm I took my second dose. All together, I enjoyed two 45 minute bathroom sessions. I wouldn’t call it pleasant, but it wasn’t much of a bother.

I went in to the procedure center at 0900 and was called back to pre-op around 0930. I changed into a gown, was connected to the monitor, received an IV, and spoke with my gastroenterologist and anesthesiologist. About 15 minutes later, I was in the procedure room. As my nurse anesthetist pushed the propofol into my IV, I made everyone in the room promise not to record anything I said under anesthesia. The next thing I remember is waking up in post-op. A few minutes later, I was able to get myself dressed and I was home by 1115. All in, I was out of the house for about 2.5 hours. I felt 100% normal for the rest of the day.

If you’ve been delaying colonoscopy, I recommend getting it done. It’s a safe and effective screening test. If you have a polyp, the doctor can remove it and prevent it from turning cancerous. If you have cancer, detecting it as early as possible is essential for successful treatment and survival. If you wait too long and your colon cancer becomes metastatic, 5-year survival rates plummet to less than 20%. The treatments also become more and more challenging.

Whether I’ve convinced you or not, I’d love to hear your thoughts, questions, and colonoscopy related experiences.

Comments 1

  1. I am meeting my colonoscopy doctor on Friday for the pre-procedure appointment. I have had a number of colonoscopies over the years and I agree with everything you wrote. The procedure sounds scarry, but the reality is that it is nothing to be feared.

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