Colonoscopy: What to Expect, Plus a Few Tips

Colonoscopy is central to the care plan for families with hereditary colorectal cancer (CRC) syndromes, as Georgia Hurst mentioned in her earlier post. Colonoscopic screening is the major means for prevention and early detection of CRC in this setting. It is worth highlighting what you can and should expect when getting a colonoscopy.  

It is clear that all colonoscopies and all colonoscopists (is that a word?) are not equal; there is surprisingly high variability in the quality of colonoscopy. The goals of screening colonoscopy include early detection of CRC while it is still curable or, better yet, prevention of CRC by finding and removing pre-cancerous polyps. The ultimate measure of screening colonoscopy quality is the rate of CRC that occurs before the next scheduled screening examination, called the interval CRC rate (ICR). ICRs are difficult to measure, but the few studies available show a substantial (2- to 15-fold) variability in ICRs among colonoscopists. This highlights the need to identify the critical components of a high-quality colonoscopy, and develop ways to measure them (metrics). 

Achieving a high-quality colonoscopy requires a joint effort by you, your endoscopist (the specialist doing the procedure) and the endoscopy unit. There is general agreement about important metrics for a high-quality colonoscopy, which include elements that occur before, during and after the procedure.

Before the procedure

The ability to identify and completely remove colonic polyps requires being able to see the entire colonic mucosa (tissue), so the prep is critical. A high-quality endoscopy suite is expected to have good or excellent quality preps for ≥ 85% of all colonoscopies. There are numerous colonoscopy preps available, but they all induce dramatic diarrhea and none of them is fun; the prep is generally considered the most unpleasant part of the exam. Better cleansing is obtained by using a split dose prep (half the night before, half the day of the procedure).

In contrast, many say that the sedation is the best part of a colonoscopy and may compensate (in part) for the diarrhea-induced sleep disturbance that happens the night before the exam.  Other pre-procedure quality metrics include an appropriate reason for the colonoscopy and proper informed consent to have the procedure.

What should you expect?

  • Diarrhea, diarrhea, diarrhea and sleep disturbance
  • Detailed information/instructions for the recommended prep. In addition to the prep protocol, this should include the dietary restrictions and a description of what you will likely experience (“When will the diarrhea start and stop?” “When will I sleep?”) and the side effects that can arise from the prep (like dehydration and vomiting).
  • To be offered the option of a split dose prep
  • To learn whether you need to change any of your medications/supplements prior to the procedure, which type of sedation will be used, and the need to arrange for transportation
  • To be told much the procedure will cost, and how much of that you will be expected to pay
  • Did I mention the diarrhea?


  • The prep is the part of the procedure that you control. You don’t want to have a poor quality examination or to have to do the prep more than once. Get the prep kit several days before your scheduled procedure; read and follow the instructions carefully.
  • Accept a split dose prep when offered – or ask about it, if it’s not offered
  • Preps vary substantially in volume, taste, and cost; there are options 
  • Propofol anesthesia is preferred over conscious sedation with drugs like fentanyl and versed by many endoscopists (and patients), but it must be administered under the direction of an anesthesiologist. It doesn’t improve the quality metrics of the examination and it can add $500-$2,000 to the overall cost of the procedure. 
  • In the U.S., The Affordable Care Act requires insurance companies to cover the cost of screening colonoscopies without co-pays. However, if a polyp is found, or the test is done to evaluate symptoms or as a second step after another type of screening test, it may be classified as a “diagnostic examination” and, depending on your insurance coverage, you may receive a substantial bill.

During the Procedure

The single most important component of a high-quality colonoscopy is having it performed by a high-quality colonoscopist – one with a low ICR. Although it currently isn’t feasible to routinely measure ICRs, another more easily measured metric, the adenoma detection rate (ADR), strongly correlates with the ICR. The ADR is the percent of average risk patients undergoing a screening colonoscopy found to have one or more colonic adenomas. It is arguably the single most important metric of a high-quality colonoscopist. The minimal acceptable ADR is  25% (≥ 20% in women, ≥ 30% in men). 

There is substantial variability (5-fold or more) in ADRs among endoscopists. In general, higher ADRs are found in those who have had more endoscopic training and those that do more colonoscopies. As a group, gastroenterologists and colorectal surgeons have more extensive training, do more colonoscopies, and have higher ADRs than internists or general surgeon colonoscopists; there are certainly exceptions to this generalization. ADRs can be improved by education and training.

Additional metrics of a high-quality colonoscopist are a high rate of examinations that are complete to the cecum (>95% for screening exams with good preps), an adequate amount of time taken examining the colonic mucosa on the way back from the cecum (average > 6 minutes), and a low complication rate (serious complications <1/1,000 procedures).

What should you expect?

  • A high-quality colonoscopy done by a high-quality colonoscopist. The colonoscopy should be complete to the cecum and adequate time should be taken to carefully examine the colon. The colonoscopist should be well trained, perform enough colonoscopies to maintain technical expertise (some suggest >200/year) and have an ADR of over (preferably well over) 30%. A high-quality colonoscopist should know and be willing (eager, in fact) to provide you with his/her training, colonoscopy volume and ADR.  


  • Colonoscopy is highly effective, but it is not perfect. The miss rate for CRCs is estimated to be 2-6% overall, and even high-quality endoscopists occasionally miss CRCs. (CRCs can be flat, inconspicuous, hidden behind folds, or covered by mucus or stool). The miss rate for precancerous polyps is higher.  
  • Colonoscopy is safe, but serious complications such as perforations and bleeding do occur rarely (<1/1000 procedures)
  • Colonoscopy is expensive. In a highly publicized (and criticized) 2013 articleThe New York Times reported costs as high as $4,000-$8,500 in cities across the country.

After the Procedure

Quality metrics after colonoscopy completion include generation of a high-quality endoscopy report and appropriate follow-up recommendations.

What should you expect?

  • To receive a copy of a high-quality endoscopy report. It should document the reason for and extent of the examination, the quality of the prep, describe all abnormalities found including the number, size, location and appearance of any polyps and how they were removed; photo-documentation of important findings is preferred. 
  • To receive instructions on the symptoms associated with serious post-colonoscopy complications and information about who to contact for questions/concerns
  • To receive your pathology results and follow-up recommendations                   


Inform your family about your colonoscopy findings. If you have a CRC or an advanced polyp, it may have implications for the cancer risk in your relatives. 



The information, including but not limited to, text, graphics, images and other material contained on this blog are for informational purposes only. The purpose of this blog is to promote broad understanding and knowledge of various health topics. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition or treatment and before undertaking a new health care regimen, and never disregard professional medical advice or delay in seeking it because of something you have read on this blog. Ambry Genetics Corporation does not recommend or endorse any specific tests, physicians, products, procedures, opinions or other information that may be mentioned on this blog. Reliance on any information appearing on this blog is solely at your own risk.


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