EDITORIAL

Inequities in colonoscopy: variation in performance andoutcomes of colonoscopy

The seminal National Polyp Study (NPS) suggested thatcolonoscopy with polypectomy can lead to as much asa 90% reduction in the subsequent risk of developing colo-rectal cancer (CRC).1 Many subsequent studies have founda lower magnitude of protection.2-5 It is likely that some ofthe difference is owing to the missed detection of adenomasand cancers at the initial examination. The initial colonos-copies in the NPS were careful examinations performedby a select group of expert endoscopists; a number of colo-noscopies were repeated within 3 months of the initial ex-amination when there was doubt about the adequacy ofclearance of the colon at the initial examination. Conversely,colonoscopies in the later studies were performed in real-world practice settings by many different endoscopistswith varying levels of training and competency.

Indeed, some studies estimate that approximately 5% ofCRCs may be missed at the initial examination.6,7 There areinherent limitations of the optical colonoscopy, witha higher chance of missing lesions behind colonic folds, assuggested by computed tomography colonography.8 How-ever, more intriguing and concerning is the occurrence ofa wide variation in the performance and outcomes of colo-noscopy among different endoscopists and different set-tings.9 In Ontario, Canada, the rates of completion ofcolonoscopy to the cecum are lower if the colonoscopy isperformed by family physicians or general internists or ifit is performed in ambulatory care centers.10 Endoscopistswho perform fewer than 100 colonoscopies each year areless likely to complete the examination to the cecum.11 Insome series, the missed cancer rate is higher for colonos-copies performed by primary care physicians or in an officeor in rural setting.6,12 Even among gastroenterologists,there may be a difference in the sensitivity of colonoscopyfor CRC detection.13 Furthermore, recent studies suggestthat there is a higher risk of associated complications ifendoscopy is performed by low-volume endoscopists.14,15

The ultimate goal of CRC screening is to reduce the bur-den of disease, as measured by CRC incidence and/or can-cer-related mortality. However, because a very largesample size of colonoscopies performed by each endoscop-ist would be required to demonstrate the potential variationin the detection of CRC, studies evaluating differences in le-

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sion detection rates among individual endoscopists haveusually focused on polyp or adenoma detection rates. Theindividual endoscopist can be a more important predictorof detecting adenomas of any size than even the age andsex of the individuals undergoing the procedures.16

Over the past few years, several investigators have triedto determine the reasons for the differences in detectionrates of colorectal lesions among different endoscopists.Withdrawal time during colonoscopy is a relatively easilymeasurable variable and has therefore become a focus. Inthis issue of GIE, Imperiale et al17 report on the analysis of

the correlation of procedure time and polyp detection ratesfrom the Eli Lily’s CRC screening program in Indiana. Theyexcluded endoscopists with the lowest volume of colonos-copies in the program (40 endoscopists who performed co-lonoscopies on 261 patients) and assessed the mean polypdetection rate as a function of the mean total proceduretime and estimated withdrawal time. The overall polyp(and adenoma) detection rate was dependent on the proce-dure time; the detection rate for larger advanced neoplasticlesions did not reach statistical significance (P Z .07). Theydid not analyze the results separately for intermediate-size(6-10 mm) polyps. Of note, the study has a serious limitationin that only aggregate data per endoscopist were analyzedand individual patient-level colonoscopy data were not re-ported. Thus, patient and procedure characteristics cannotbe adequately analyzed. In addition, the regression analysespresented may not accurately estimate the statistical signif-icance or fractions of variance explained by procedure timebecause the inherent variations in individual patient charac-teristics and outcomes are not taken into account. Anotherlimitation is that the primary variable of interest, the with-drawal time, was not measured directly, but was extrapo-lated from the total procedure time by subtracting 8minutes, which was arbitrarily assumed to be the insertion

The ultimate goal of colorectal cancer screen-ing is to reduce the burden of disease, as mea-sured by colorectal cancer incidence and/orcancer-related mortality.

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Singh & Singh Editorial

time for each colonoscopy. It is possible that some endo-scopists may have a faster insertion time but then take lon-ger to withdraw the colonoscope compared with otherswho may have the same overall total procedure time butspend a larger proportion of time on insertion. The authorsdid not adjust the P values for multiple comparisons, whichwould also tend to exaggerate statistical significance. Con-versely, although their findings should be considered ex-ploratory in nature, the data are based on a large numberof colonoscopies.

In contrast to the current study, Barclay et al,18 using in-dividual patient data, found a significant association be-tween variation in the advanced neoplasia detection rateand withdrawal time. Moreover, Barclay et al,19 in a follow-up study, demonstrated an increased detection rate of ad-vanced neoplasia by implementing a protocol of a minimumof 8 minutes for colonoscope withdrawal. In another recentstudy, there was a significant association of polyp detectionrate with withdrawal time for polyps smaller than 5 mm.20

However, when the baseline polyp detection rate is high,implementing a policy of a minimum of 7 minutes for colo-noscope withdrawal in an academic medical center may notlead to improved polyp detection rates.21

The value of removing small adenomas, the detectionrate of which varies the most among endoscopists, needsto be better defined. However, the current recommenda-tions are to remove all adenomatous polyps found at colo-noscopy.22 Although most small polyps are benign and willtake years to grow, many individuals will not return for re-peat colonoscopy. Moreover, the results of NPS and themodeling studies are based on removal of all detected ade-nomas at baseline.

Adequate withdrawal time is only one of the characteris-tics of complete colonic examination. Colonoscopy comple-tion to the cecum, adequate bowel preparation (featuresthat were not commented on in the current study descrip-tion), and adequate visualization of colonic mucosa arewell-recognized important additional features. Adequatecolonic distention and removal of residual fluid allow bettervisualization of colonic mucosa, improving the adenoma de-tection rates.23 However, there are no large studies evaluat-ing the variation in different aspects of withdrawaltechnique and mucosal examination among different endo-scopists. The Quality Assurance Task Group of the NationalColorectal Cancer Roundtable recently developed a stan-dardized colonoscopy reporting system to document varia-tion in performance of colonoscopy and to developbenchmarks for the various indicators.22 This system willlikely evolve; for example, one recommendation is to obtaincecal photographs to document the cecal intubation, eventhough video recording provides much more convincingevidence for the uninvolved reviewers.24

The perceived adequacy of the endoscopic examinationnot only affects the subsequent risk of developing CRC, butalso the recommendation for the screening intervals. In theUnited States, the Multisociety Task Force recommends

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flexible sigmoidoscopy at 5-year intervals because of theconcern about the adequacy of the examination in the usualclinical practice, even though there is evidence to suggestthat longer intervals may be adequate.25 Two case-controlstudies suggest that the protective effect of sigmoidoscopypersists for at least 10 years.26,27 Flexible sigmoidoscopiesare performed at 10-year intervals in the Colon Cancer Pre-vention Program of Kaiser Permanente. The Prostate, Lung,Colorectal, and Ovarian Cancer Screening Trial in the UnitedStates is evaluating flexible sigmoidoscopy every 5 years. Incontrast, in Europe, once-in-a-lifetime flexible sigmoidos-copy is being evaluated in 2 clinical trials.28

There is evidence to suggest that benefits of colonoscopymay last longer than 10 years.29,30 Modeling with data fromthe NPS suggests that the initial colonoscopy is the most im-portant examination.31 Another recent modeling study,based on autopsy data, predicts that approximately 80% ofindividuals presenting with CRC between the ages of 50and 80 already have an adenoma in their colon at age 50.In this model, the majority of CRCs can be prevented by a sin-gle colonoscopy at age 50, followed by surveillance of thosewith adenomas.32 For those at average risk of developingCRC and if the initial colonoscopy is negative for colorectalneoplasia, it may be time to consider the strategy of once-in-a-lifetime colonoscopy. Currently, the United States,Germany, and Poland are among the very few countries pur-suing widespread screening colonoscopy outside researchprotocols.28 Once-in-a-lifetime colonoscopy (if negative)will likely make screening colonoscopy feasible for mostother countries and may provide the greatest benefit, evenin countries currently pursuing screening colonoscopy be-cause resources could then be directed toward the initialscreening instead of surveillance of individuals with a lowrisk of CRC (and hence increase screening rates, even with-out additional resources). However, such strategies can onlybe considered if the inequities in the performance of thecolonoscopies can be reduced, resulting in more uniformoutcomes after the procedure. In fact, at least 2 recent pop-ulation-based studies have highlighted the fact that colono-scopic screening as practiced in the community does notalways provide adequate protection against CRC detectionor mortality, especially for right-sided tumors.33,34 Singhet al,33 in a large case-control study of colonoscopies in theCalifornia Medicaid population, found that the relative riskof CRC after a negative colonoscopy (compared with noscreening) was 0.55 (95% CI, 0.16-0.65), but there were largedifferences between left- and right-sided lesions. The rela-tive risk for left-sided tumors after a negative colonoscopywas 0.16 (95% CI, 0.09-0.28), whereas that for right-sidedlesions was a far more modest 0.67 (95% CI, 0.51-0.88).33

The beneficial effects of sigmoidoscopy were considerablysmaller.33 Baxter et al34 studied the practice of colonoscopyin Ontario, Canada, in another case-control study and con-cluded that the beneficial effect of screening colonoscopyon mortality from CRC was confined to the left-sided tumorsonly.

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Editorial Singh & Singh

Colonoscopic CRC screening cannot eliminate allsubsequent risk of developing CRC, but we can certainlyimprove the current effectiveness in the routine clinicalpractice by improving the quality of the examinations.Whether the optimal withdrawal time to allow complete vi-sualization of colonic mucosa for an average endoscopistshould be 6 or 10 minutes or another time interval stillneeds to be better defined. Optimal withdrawal is essentialto ensure complete colonic examination. Spending 6 or 10minutes during withdrawal is a small price to pay forimproving outcomes after colonoscopy.

DISCLOSURE

All authors disclosed no financial relationships rele-vant to this publication.

Harminder Singh, MD, MPHDepartments of Internal Medicine and Community Health

SciencesUniversity of Manitoba

Winnipeg, Manitoba, CanadaGurkirpal Singh, MD

Division of Gastroenterology and HepatologyDepartment of Medicine

Stanford University School of MedicinePalo Alto, California

Abbreviations: CRC, colorectal cancer; NPS, National Polyp Study.

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