Background: Prior guidelines recommended initiating colorectal cancer (CRC) screening for average-risk individuals at age 50 years; however, recent guidelines have made qualified recommendations to initiate screening at age 45. In 2022, Kaiser Permanente health systems in Northern California (KPNC), Southern California (KPSC), Colorado (KPCO), and Washington (KPWA) implemented fecal immunochemical test (FIT)-based screening starting at age 45 years. This study sought to evaluate FIT uptake (completion) within 3 months after FIT kit distribution, FIT positivity (positive test result), colonoscopy within 3 months after a positive FIT, and FIT-positive colonoscopy yield in patients ages 45-49 versus 50 years of age in these health systems.

Methods: Data on FIT uptake and positivity and colonoscopy follow-up and outcomes for FIT kits distributed between January through September 2022 were assessed from electronic health records. Only patients offered CRC screening for the first time were included. Differences between age groups (represented as unadjusted risk ratios [RR]) were evaluated using robust modified Poisson regression.

Results: Of 405,787 FIT kits distributed, 312,192 (76.9%) were to those ages 45-49 years and 93,595 (23.1%) to those 50 years of age (Table 1). FIT uptake within 3 months was slightly higher in the younger compared to older age group (43.6% vs. 41.5%; unadjusted RR: 1.05, 95% confidence interval (CI): 1.04-1.06) (Table 2). Those 45-49 had a slightly lower FIT positivity than those age 50 years (4.5% vs. 4.8%; RR:0.94, 95% CI: 0.89-0.98) and the frequency of colonoscopy follow-up within 3 months after a positive FIT was similar between the age groups (68.7% vs. 69.0%; RR: 1.00, 95% CI: 0.96-1.03). The detection of any adenoma was modestly less frequent among those 45-49 versus 50 years of age (50.3% vs 56.7%; RR: 0.89, 95% CI: 0.84-0.94). Other colonoscopy findings did not differ significantly between the two groups, including adenoma with advanced histology (12.3% vs. 13.7%; RR: 0.90, 95% CI: 0.76-1.05), polyp with high-grade dysplasia (3.1% vs 4.0%; RR: 0.76, 95% CI: 0.55-1.04), sessile serrated lesion (8.1% vs 8.5%; RR: 0.95, 95% CI: 0.77-1.16), and CRC (2.5% vs, 2.3%; RR: 1.11, 95% CI: 0.74-1.67).

Discussion: FIT uptake and positivity and FIT-colonoscopy follow-up and yields were generally similar in those ages 45-49 versus 50 years of age. These data provide support for the recommendation to initiate CRC screening starting at age 45 years and can help inform efforts to implement and plan for earlier FIT-based screening.

Brian Hixon

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