Your colonoscopy may not be as good as you think – Why ADR (adenoma detection rate) matters

ADR or adenoma detection rate is a quality measure for the effectiveness of colonoscopy. It is a measure of how good your doctor is at finding adenoma polyps in patients who undergo colon cancer screening.[i] This information is often collected by the people who run the endoscopy center. There is a wide variation between colonoscopists in terms of their skills at detecting adenomas, expressed as the ADR: 7.35 % – 52.5 %.[ii] In other words, the best are seven times more likely to find at least one polyp during a screening colonoscopy then the worst.

Polyps can get missed and may turn into cancer before your next colonoscopy.

What does ADR (adenoma detection rate) have to do with colon cancer?

Imagine that you just had a colonoscopy and you had one or even a few polyps, but your doctor did not see any. She may therefore tell you to come back in 5 years. At 5 years you get another colonoscopy and there is a big cancer. Something we wanted to prevent with colonoscopy. This type of cancer is known as “interval cancer”. The number of interval cancers (which can probably never be completely avoided) is higher (worse) when the colonoscopist has a low ADR. Makes sense as most colon cancers were a polyp first. Conversely, if your doctor is good at finding polyps, the chances of you getting an “interval cancer” are lower.  In a primary colonoscopy screening setting, a 1 % increase in ADR predicted a 3 % decrease in the risk of interval colon cancer.

Why do some doctors have a higher ADR (adenoma detection rate)?

Flat polyps like this one can be missed.

The short answer is that they spent more time looking for polyps. Longer mean withdrawal times (time spent actually scrutinizing the lining of the colon) were associated with higher adenoma detection rates. The ADR increased by 3.6 % per every extra minute used for withdrawal.[iii] Withdrawal times do not have to be excessively long, as there are few gains after 10 minutes have been reached. This all refers to averages and some colons just take more time to properly examine.
This raises the issue of factors that are hard to measure, such as ‘diligence’. Doug Rex, an internationally known colonoscopy expert, says: “State of the art awareness of the disease spectrum, combined with obsessive-compulsive examination technique, are sufficient to create a very efficient [polyp] detector.” However, there are also a number of technological advances which may improve the ADR even more and interested readers are referred to Dr. Rex’s article.[iv]

So how do I know whether my colonoscopy doctor is doing a good job?

You could ask what his or her ADR (adenoma detection rate) or average withdrawal time is. Any evasive answer would not be a good sign. In contrast, enthusiasm in discussing this topic with you, would be reassuring. The current targets for ADR are 30% in men and 20% in women, or 25% for a typical mixed-gender patient population, and many U.S. endoscopists now exceed those minimum thresholds by a substantial margin.

You may also ask “What have you done to increase your adenoma detection rate”? Again, the obsessive-compulsive examiner would be happy to tell you. Conversely, if your colonoscopy doctor seems to be offended by the question, you should be concerned. [v]


[i] The technical definition is: The adenoma detection rate (ADR) is the percentage of patients aged ≥50 years undergoing first-time screening colonoscopy who have one or more conventional adenomas detected and removed.

[ii]  Corley DA, Jensen CD, Marks AR. et al. Adenoma detection rate and risk of colorectal cancer and death. NEJM 2014; 370: 1298-1306

[iii] Shaukat A, Rector TS, Church TR. et al. Longer withdrawal time is associated with a reduced incidence of interval cancer after screening colonoscopy. Gastroenterology 2015; 149: 952-957

[iv]  D. Rex. Improving the Adenoma Detection Rate. Gastroenterology & Endoscopy News. 2017.

[v] D. Rex. Yes, You Can! — Improve Your ADR and Reduce Your Patient’s Colorectal Cancer Risk (So Why Are You Waiting?) NEJM Journal Watch. May 15, 2017

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