Serrated polyps are diverse lesions that encompass hyperplastic polyps (HPs) proximal to the rectum, sessile serrated lesions (SSLs) with or without dysplasia, and traditional serrated adenomas (TSAs)¹. Although most sporadic colorectal cancers (CRCs) arise from adenomas, it is believed that about 15-30% of CRCs² arise through an alternate serrated neoplasia pathway. This is particularly true for proximal and interval cancers. Serrated lesions can be flat, with a mucous cap, and are easily missed compared to adenomas. Improving detection rates is crucial to reducing CRC incidence and mortality.

We aim to compare the ability to detect sessile serrated lesions with high definition scopes (HD) versus standard definition scopes (SD) in a faecal immunochemical test (FIT) – positive national screening cohort.

A retrospective analysis was conducted of 400 BowelScreen (NCSS) participants in Ireland’s national colorectal screening program who underwent colonoscopy after a positive faecal immunochemical test (> 45 ug/g) and had polyps removed. All colonoscopies were performed by a BowelScreen endoscopist. They were evenly split between HD and SD. Detection rates were calculated for SSLs and HPs, and statistical analysis was performed with chi-square testing with a two-sided significance level of α=0.05. Adenomas, serrated lesions with dysplasia, traditional serrated adenomas and identifying serrated polyposis syndromes were also assessed in this cohort.

The mean age of the cohort was 66.6 years, with data collected between 2018 and 2025. Among 200 HD scopes performed, 30 SSLs were detected (15%) compared to 25 in the SD group (12.5%) (p = 0.561). For hyperplastic polyps, 51 HD scopes detected HPs (25.5%) compared to 37 (18.5%) in SD (p = 0.117). One SSL with dysplasia was detected in the HD arm, and 1 TSA was detected in each arm. It is worth noting that there was one patient in whom serrated polyposis syndrome was diagnosed with a high-definition endoscope. No observed statistical significance achieved.

Although this initial retrospective analysis did not show statistical significance, an observed higher absolute detection rate of serrated lesions with HD scopes suggests a potential benefit. Post hoc power considerations indicate that a substantially larger sample size would be required to reflect the actual technology effect. Key limitations include the lack of standardised withdrawal times and unmeasured variation in bowel preparation quality, especially in the proximal colon, which can affect lesion detection rate. Given the established contribution of serrated lesions to proximal and interval CRC, and emerging quality metrics such as SSL detection rate, prospective, adequately powered studies are needed to clarify if HD colonoscopy should be mandated as standard, especially for population-based screening programmes.