Colonoscopy is the cornerstone of colorectal cancer (CRC) prevention worldwide and in the United States (1-4). In the United States, colonoscopy is commonly used for primary CRC screening and is the first and preferred colorectal imaging test in patients presenting with symptoms, with positive screening tests other than colonoscopy (1-4), undergoing surveillance after resection of CRC or precancerous polyps (5,6), with a strong family history of CRC or advanced precancerous lesions (1), and undergoing dysplasia surveillance in ulcerative colitis (UC) and Crohn's colitis (7).Evidence indicates colonoscopy reduces the incidence of CRC and prevents CRC mortality (8-23) (Table 1). Reduction in incidence and mortality of CRC with colonoscopy is greater in the left-sided colon than the right-sided colon (24). In the first randomized controlled trial comparing colonoscopy with no screening, patients who complied with and underwent colonoscopy (per-protocol analysis) had a 31% reduction in CRC incidence and a 50% reduction in CRC mortality (25). Several factors, including earlier than planned reporting of trial results, absence of stage shift in CRCs detected in the colonoscopy arm (suggesting symptomatic patients were enrolled in the colonoscopy arm), and lower than expected cecal intubation and adenoma detection, indicate the study may have underestimated the benefits of colonoscopy (25).The impact of colonoscopy on CRC and other outcomes (e.g., polyp detection, assignment of screening, and surveillance intervals) is highly operator-dependent. Detection of precancerous colorectal lesions is highly variable (26-28) and is associated with the risk of developing post colonoscopy CRC (PCCRC) (21,22). In response to evidence of inconsistent performance, professional gastroenterology and endoscopy societies began an organized movement 2 decades ago to improve the quality of technical performance and reduce the operator-dependence of colonoscopy (29). This document represents the latest update of recommendations from the American College of Gastroenterology (ACG)/American Society for Gastrointestinal Endoscopy (ASGE) Quality Task Force. Previous recommendations from this task force were published in 2006 (30) and 2015 (31). This update reflects new evidence published since 2015.High-quality colonoscopy includes adequate bowel preparation, safe colonoscope insertion to the proximal extent of the colon, detailed examination with identification of all precancerous lesions, and complete and curative resection of these lesions. The process is completed by thorough and accurate documentation of findings and assignment of any appropriate screening or surveillance follow-up at cost-effective intervals based on recommendations from the US Multi-Society Task Force (MSTF) on CRC (32). High-quality performance in 1 aspect of colonoscopy does not ensure adequate performance in others. For example, colonoscopists may be effective at detection but not resection of precancerous lesions or vice versa (33). Understanding deficiencies in perfor...
