Abstract Introduction Inflammatory bowel disease (IBD) and colorectal cancer (CRC) share overlapping symptoms. Faecal Immunochemical Test (FIT) is mandated in UK primary care to triage symptomatic patients suspected of CRC, but the extent to which IBD is identified in these patients remains unclear. We aim to assess the one-year IBD diagnosis rate in symptomatic patients following FIT for suspected CRC, and how this varies with age, FIT, and faecal calprotectin (FCP). Methods A population-based cohort study of symptomatic patients undergoing FIT in the UK Clinical Practice Research Datalink (CPRD) (January 2019-June 2023), with one-year follow-up was conducted. Kaplan-Meier estimates were used to assess cumulative one-year IBD-risk, stratified by age, FIT, and FCP results. Results 2762 of 473402 (0·58%) patients were diagnosed with IBD within one-year of FIT. Patients under 50 years (N=110501) accounted for 53·6% of all IBD diagnoses, but only 6·9% of all CRC diagnoses (N=347). Overall IBD-risk was 2·3% with FIT≥10µgHb/g compared to 0·1% with FIT10µgHb/g. Among 63469 patients with elevated FCP and FIT, IBD-risk in those under 50 years was 21·0% when FIT≥10µgHb/g and FCP50µg/g. The combined risk of CRC or IBD in those with FIT≥10µgHb/g was 7·1%. This fell to 3·3% in the subset of patients who also had FCP ≤50µg/g. Conclusion IBD is more common than CRC in patients under 50 years referred on symptomatic FIT pathways using a FIT≥10µgHb/g threshold. In a selected cohort of dual-tested patients, FCP provided additional risk stratification. Incorporating routine FCP into symptomatic FIT pathways may better target further investigations.
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