Diagnosis of inflammatory bowel disease after symptomatic faecal immunochemical testing: population-based cohort...

Inflammatory bowel disease (IBD) and colorectal cancer (CRC) share overlapping symptoms. Faecal immunochemical testing (FIT) is mandated in UK primary care to triage symptomatic patients suspected of having CRC, but the extent to which IBD is identified in these patients remains unclear. The aim of this study was to assess the 1-year IBD diagnosis rate in symptomatic patients after FIT for suspected CRC and how this varies with age, FIT level, and faecal calprotectin (FCP) result.

A population-based cohort study of symptomatic patients who underwent FIT in the UK Clinical Practice Research Datalink (CPRD) (January 2019-June 2023) with 1-year follow-up was conducted. Kaplan-Meier estimates were used to assess cumulative 1-year IBD risk, stratified by age, FIT level, and FCP result.

Of 473 402 patients, 2762 patients (0.58%) were diagnosed with IBD within 1 year of FIT. Patients aged <50 years (110 501 patients) accounted for 53.6% of all IBD diagnoses (1481 patients), but only 6.9% of all CRC diagnoses (347 patients). Overall IBD risk was 2.3% with FIT ≥10 µg Hb/g compared with 0.1% with FIT <10 µg Hb/g. Among 63 469 patients with elevated FCP results and FIT levels, IBD risk in those aged <50 years was 21.0% with FIT ≥10 µg Hb/g and FCP >50 µg/g. The combined risk of CRC or IBD in those with FIT ≥10 µg Hb/g was 7.1%. This fell to 3.3% in the subset of patients who also had FCP ≤50 µg/g.

IBD is more common than CRC in patients aged <50 years referred on symptomatic FIT pathways using FIT ≥10 µg Hb/g. In a selected cohort of dual-tested patients, FCP results provided additional risk stratification. Incorporating routine FCP testing into symptomatic FIT pathways may better target further investigations.