Posted on January 13, 2022

Slow Down to Speed Up Quality: Longer Withdrawal Time of 9 Versus 6 Minutes Increases
Adenoma Detection Rate

Jennifer M. Kolb MD, MSCS1 and Aasma Shaukat, MD, MPH, FACG2

1Assistant Professor of Medicine, Division of Gastroenterology, Hepatology and Parenteral Nutrition, VA Greater Los Angeles Healthcare System, and David Geffen School of Medicine at UCLA, Los Angeles, CA
2Robert M. and Mary H. Glickman Professor of Medicine, Director of Outcomes Research, Division of Gastroenterology, NYU Langone School of Medicine, New York, NY


This article reviews Zhao S, Yang X, Wang S, et al. Impact of 9-Minute Withdrawal Time on the Adenoma Detection Rate: A Multicenter Randomized Controlled Trial. Clin Gastroenterol Hepatol 2020 2020 Nov 19:S1542-3565(20)31553-6.

Correspondence to Jennifer M. Kolb, MD, MSCS, Associate Editor. Email:

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Question: Is adenoma detection rate higher with a minimum withdrawal time of 9-minutes versus 6-minutes?

Setting: Twelve endoscopy centers in China.

Patients: Included 1,027 outpatients (52.3% men, mean age 56.5 – 56.8) presenting for diagnostic (67.3%), screening (18.8%) or surveillance colonoscopy (14.0%) between January 2018 to July 2019. Patients with inadequate bowel preparation or failed cecal intubation were excluded.

Interventions/Exposure: Outpatients were randomized to get a minimum withdrawal time (WT) of 6 or 9 minute after cecal intubation. Using a timer, minimal WT was 2 or 3 minutes per segment (right, transverse, and left colon). Time used for biopsy or polypectomy was excluded from WT. A timer went off at pre-specified reminder intervals 1 minute before each assumed endpoint, but the endoscopist could extend WT if desired.

Outcome: Adenoma detection rate (ADR) overall and classified by anatomic location, polyp size, morphology, histology, as well as polyp detection rate, number of adenomas per colonoscopy, and adverse events.

Data Analysis: Intention-to-treat analysis and per protocol for all outcomes. Outpatients with an extended WT due to difficult exam or long colon were included in the ITT analysis but excluded from the perprotocol analysis. Comparison of means and percentages by student t and X2 Fisher exact test respectively, Mantel-Haenzel test to examine differences in subgroups, and multivariate regression to evaluate risk factors for ADR.

Funding: Grant support from National Key R&D Program of China, National Natural Science Foundation of China Shu Guang project of Shanghai Municipal Education Commission and Shanghai Education Development Foundation, Three Engineering Trainings Funds in Shenzhan.

Results: In the ITT analysis, mean WT was 6 min 15 sec + 40 sec and 8 min 53 sec + 51 sec in 6 and 9 minute WT groups, respectively (Table 1). Minimum 9-minute WT was superior to minimum 6-minute WT for ADR overall (36.6% vs 27.1%, P=0.001), proximal colon ADR (21.4% vs 11.9%, P<0.001) and ADR among less experienced (1,000-3,000 colonoscopies performed) endoscopists (36.8% vs 23.5%, P=0.001). On multivariate  logistic regression, 9-minute WT was an independent predictor of increased ADR (P=0.005). Advanced adenoma detection rate and sessile  serrated lesion detection rate were numerically higher in the 9-minute WT group but did not achieve statistical significance.

Table 1. Summary of Findings



Why Is This Important?
Professional society guidelines recommend a mean colonoscopy WT of >6 minutes for average-risk CRC screening colonoscopies without polypectomy or biopsy to ensure adequate time for thorough inspection and detection of precancerous polyps.1 This recommendation is primarily supported by a seminal retrospective database study of colonoscopies performed in 2003-04, which found that endoscopists with WT >6 minutes had higher ADR compared to endoscopists with WT <6 minutes (28.3% vs 11.8%, P<0.001). This well-established quality metric is critical to ensure the effectiveness of colonoscopy because it is a surrogate of time spent inspecting and ensures adequate time to identify adenomas. A longer WT seems to provide additional opportunity forfinding polyps and indeed studies have indicated higher ADR with longer WT up to 11 minutes.2,3 However, the data is mixed, and other studies show no incremental benefit or a ceiling effect. A recent systematic review and meta-analysis of 9 studies (2 RCTs, 2 cancer registries, 3 retrospective studies) including 69,551 patients showed higher odds of adenoma detection with a >9 min versus 6-9 minute WT (OR 1.54, 95%CI 1.30-1.82).4 Additionally, sessile serrated lesion detection rate was also higher with >9 minute versus 6-9 minute WT. This is particularly important since sessile serrated lesions in the right-side of the colon are flat, easy to miss, and are a common precursor lesion for interval CRC. Zhao et al. present the first large multicenter prospective RCT to address this question of optimal WT.

This interaction between WT and ADR is crucial since we know that higher ADRs are associated with lower rates of interval CRC.5 Also, the performance target is ADR > 25%, so an ADR of 25% should be considered a minimum acceptable ADR. Endoscopists should aspire to higher ADRs since every 1% increase in ADR has been associated with an additional 3% reduction in risk of interval CRC. Thus, if your ADR is 25-30%, then it’s probably worthwhile to consider interventions to increase your ADR, including longer WT. In a large community-based study with approximately 77,000 screening colonoscopies, withdrawal time of >6 minutes was shown to be independently associated with a reduced risk of post colonoscopy colorectal cancer (despite an adequate ADR).6

Key Study Findings
Colonoscopy with longer minimum WT of 9 versus 6 minutes significantly improved the ADR and adenomas per colonoscopy, especially in the proximal colon and among less experienced colonoscopists. Sessile serrated lesion detection rate and advanced adenoma detection rate were numerically higher in the 9-minute WT group, but these differences were not statistically significant. Notably, when a 6-minute WT was used, endoscopists achieved an acceptable ADR (27.1%), but ADR surpassed 35% when a 9-minute WT was enforced.

The study population was heterogenous with mostly diagnostic exams and only 17%-20% were screening exams, which is the typical population for calculating ADR. Although recent studies suggest that ADR can be interpreted in a mixed group, the impact of WT on true screening did not quite achieve statistical significance (30.5% vs 42.9%, P=0.08), which reflects that the study was underpowered for this group. The study was unblinded and the authors were aware of the study hypothesis which may play a role in careful inspection.

My practice
Results of this study indicate that the benefit of a longer withdrawal time is particularly advantageous for less experienced colonoscopists but may be less impactful for an individual who has been practicing for many years and already has a high ADR. These findings resonate with us. Using an audible timer, or the timer on the monitor in the procedure room is a good exercise to get in the habit of spending at least 6-8 minutes during withdrawal, and at least 2 minutes per segment.

It is important to remember that the time spent on withdrawal is meant to be used for careful segmental inspection. In my practice, I (JK) prioritize techniques for a high-quality exam such as thorough washing to remove mucus especially in the right colon where serrated lesions hide, a second look in the right colon, detailed inspection behind folds, and possible use of a distal attachment device. My WT is routinely longer than 9 minutes since I’m very thorough when scoping and I often scope with GI fellows.

In my practice (AS), we generate quarterly report cards for each endoscopist, and data for the whole group is aggregated. We strive for an ADR of  >35%, but more important is to identify anyone below 25% and provide them tools to improve. There are many interventions that improve ADR,  ranging from technique, technology and educational interventions. Improving withdrawal time and technique leads to improvement in ADR, but may have benefit in reducing post colonoscopy colorectal cancer even when the ADR is adequate. Ensuring adequate preparation, using water exchange,  and changing the patient position during the exam are additional low cost but effective interventions to consider. If further improvement is desired, I would recommend trying a distal attachment device, which helps expose more mucosa and identify polyps. It is important to be receiving regular  feedback, such as report cards during these phases and being patient but persistent!

For Future Research
There is minimal research about interventions to help endoscopists with ADR < 25%. Simply prolonging WT won’t be helpful if withdrawal technique is poor, so studies assessing impact of longer WT in those poor performing endoscopists would be helpful. Since we have multiple tools and interventions to improve ADR, studies are needed to understand the role of combining these interventions with withdrawal time and technique to understand improvement in ADR, such as distal attachment device plus enhanced withdrawal, or artificial intelligence plus a distal attachment device compared to withdrawal time alone.


  1. Rex DK, Schoenfeld PS, Cohen J, et al. Quality indicators for colonoscopy. Am J Gastroenterol 2015;110:72-90.
  2. Butterly L, Robinson CM, Anderson JC, et al. Serrated and adenomatous polyp detection increases with longer withdrawal time: results from the New Hampshire Colonoscopy Registry. Am J Gastroenterol 2014;109:417-26.
  3. Barclay RL, Vicari JJ, Greenlaw RL. Effect of a time-dependent colonoscopic withdrawal protocol on adenoma detection during screening colonoscopy. Clin Gastroenterol Hepatol 2008;6:1091-8.
  4. Bhurwal A, Rattan P, Sarkar A, et al. A comparison of 9-min colonoscopy withdrawal time and 6-min colonoscopy withdrawal time: A systematic review and meta-analysis. J Gastroenterol Hepatol 2021; 36(12):3260-67.
  5. Corley DA, Jensen CD, Marks AR, et al. Adenoma detection rate and risk of colorectal cancer and death. N Engl J Med 2014;370:1298-306.
  6. 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;149:952-7.

Kolb January 2022