Monitoring Colorectal Cancer Screening at Scale: Conformance Checking and Bottleneck Detection in Northern Portugal

ObjectiveTo evaluate follow-up after positive faecal immunochemical test (FIT) results in a population-based colorectal cancer screening programme and identify pathway drift and operational bottlenecks relevant to primary care coordination.MethodsWe conducted a retrospective descriptive service evaluation using time-stamped administrative event-log data from the Northern Region of Portugal. The full dataset covered 2018 to 2025 and included 6.96 million events from 1.18 million invited individuals. The main comparative analysis used incident screening episodes starting in 2022-2023 (n = 320 330) and 2024-2025 (n = 135 213), each followed for 365 days from invitation mailing. Key variables were pathway variants, conformance precision, alignment cost, and dwell time between operational steps from invitation to colonoscopy-related activity.ResultsThree dominant variants accounted for more than 95% of episodes in both cohorts. Precision for the 2024-2025 cohort was 0.65 against its own model but fell to 0.45 when assessed against the 2022-2023 baseline model, indicating behavioural drift despite fitness remaining close to 1.00. Median alignment cost remained low overall (7-11 normalised units), but p90 values of 11-16 showed that deviations were concentrated in subsets of cases. Among FIT-positive episodes entering primary care follow-up, approximately 60% proceeded to colonoscopy within 365 days. Dwell time for the FIT mailed to FIT returned transition increased by 31% in the POST cohort, and laboratory result-to-follow-up transitions also lengthened.ConclusionsRoutine pathway monitoring identified incomplete follow-up after positive FIT results and operational drift not captured by conventional participation indicators alone. These findings support targeted action in primary care and programme management, particularly reminder systems, referral tracking, and protected capacity for timely diagnostic colonoscopy.