Polyp and Adenoma Detection Rates in the Proximal and Distal Colon

Erika S Boroff MD; Suryakanth R Gurudu MD; FACG; Joseph G Hentz; Jonathan A Leighton MD; FACG; Francisco C Ramirez MD; FACG


Am J Gastroenterol. 2013;108(6):993-999. 

In This Article

Abstract and Introduction


Objectives: Little is known about the correlation between the polyp detection rate (PDR) and the adenoma detection rate (ADR) in individual colonic segments. The adenoma-to-polyp detection rate quotient (APDRQ) has been utilized in retrospective study as a constant to estimate ADR from PDR. It has been previously stated that diminutive polyps in the rectum are more likely to be non-adenomatous, compared with more proximal segments, yet the APDRQ uses data from the entire colon. We sought to characterize and compare ADR and PDR in each colonic segment, estimate ADR using the conversion factor, APDRQ, and assess the correlation between estimated and actual ADR for each colonic segment.

Methods: As part of a quality improvement program, a retrospective chart review was conducted of all outpatient colonoscopies performed by 20 gastroenterologists between 1 October 2010 and 31 March 2011 at a single academic tertiary-care referral center. PDR, ADR, and the APDRQ were calculated for each gastroenterologist, using data from the entire colon and then for each colonic segment separately. Actual ADR was compared with estimated ADR based on the measured APDRQ.

Results: During 1,921 colonoscopies, 2,285 polyps were removed; 1,122 (49%) were adenomas. The mean (s.d.) PDR for the group was 49% (12.4%) (range, 16–64%). The mean (s.d.) ADR was 31% (7.4%) (range, 13–42%). PDR and ADR correlated well in segments proximal to the splenic flexure, but diverged in distal segments. ADR was significantly higher in the right colon (17.1%) than in the left (13.5%) (P=0.001). The correlation between estimated and actual ADR using the APDRQ was significantly higher in the right colon (r=0.95 (95% confidence interval (CI), 0.87–0.98)) than in the left (r=0.59 (95% CI, 0.17–0.83)) (P<0.05).

Conclusions: Although PDR and ADR correlate well in segments proximal to the splenic flexure, they do not correlate well in the left colon. Caution should be exercised when using PDR as a surrogate for ADR if data from the rectum and sigmoid are included.


Colonoscopy is regarded as an effective tool to reduce the incidence of colorectal cancer (CRC) and its associated mortality.[1,2,3] The protection afforded by colonoscopy is believed to be due to the detection and removal of adenomatous polyps, from which most CRCs are derived.[4–6] There is, however, considerable variation in adenoma detection among endoscopists, which indicates the need for better standards of quality in colonoscopy and methods for quality improvement.[3,5–11] The adenoma detection rate (ADR) is a validated measure of quality in colonoscopy.[12] The US Multi-Society Task Force on Colorectal Cancer, which included the American Society of Gastrointestinal Endoscopy and the American College of Gastroenterology published target ADRs for endoscopists screening asymptomatic men and women with colonoscopy.[8] Colonoscopies performed by endoscopists with higher ADRs are associated with lower rates of interval cancer.[12] Measuring the ADR has been deemed central to improving the performance of endoscopists with low detection rates.[9,10,13]

Unfortunately, the ADR is cumbersome to obtain because of the lack of automated interfaces between pathology and endoscopy databases, which represents a challenge to many practices. In contrast, the polyp detection rate (PDR) is readily available from endoscopy reports and has been suggested as a surrogate for ADR.[14,15] The rationale for using PDR is that a relatively constant percentage of polyps removed by an endoscopist are adenomatous; thus, multiplying the PDR by this percentage as a conversion factor provides an estimate of the endoscopist's ADR. Using this method, Francis et al.[14] conducted a retrospective study and found a good correlation between estimated ADR and actual ADR. At issue is whether prospective data collection of PDR without actual measurement of ADR will reduce the accuracy of PDR over time, as polypectomy rates increase to meet guidelines.[8]

Both PDR and ADR are calculated and reported for the entire colon, but recent studies have demonstrated that the protective effect of colonoscopy against CRC is not uniform throughout the colon, and that there is a lower rate of protection in the right colon.[1,16,17] Interval cancers may also represent lesions that were missed on the index colonoscopy.[18–21] Determining whether PDR and ADR ratios differ in the right colon compared with those in the left colon is critical if we are to improve the level of protection afforded by colonoscopy in each segment. We therefore sought to describe the distribution of adenomas detected throughout the colon, to measure PDR and ADR in each colonic segment, and to evaluate the association of PDR and ADR in the right colon vs. that in the left colon.