Prediction tool for early identification of patients at risk of Crohn's disease in perianal fistulas and abscesses (PREFAB): Analysis of a prospective pilot study at a non-academic, teaching centre in the Netherlands.

BACKGROUND: The aim of this study was to identify patients at risk of Crohn's disease (CD) when presenting with perianal disease and to prospectively identify clinical characteristics ('red flags') associated with CD. METHODS: All consecutive patients ≥ 16 years presenting with a perianal abscess (PAA)/fistula (PAF) between January and December 2022 were prospectively included. Faecal calprotectin (FCP) was measured in all patients, and patients were screened for potential red flags associated with CD by the use of a perianal red flags index (pRFI)-questionnaire. Colonoscopy was performed when FCP ≥ 150 mcg/g. RESULTS: Overall, 115 patients were included (median age 38 years; IQR 28-53), 55 with PAA (48%) and 60 with PAF (52%). In total, 19 patients had FCP levels ≥ 150 mcg/g (median 381 mcg/g; IQR 191-1040), and were referred for colonoscopy, of which 10 were diagnosed with CD (9% of all patients; 17% of patients with PAF). Of all patients with PAF < 40 years, 29% were diagnosed with CD (9/31). During a minimal follow-up of 2 years, two colonoscopies were performed in patients with clinical suspicion for CD, demonstrating CD in 1 patient, resulting in a total of 11/115 patients with CD (10%), all presenting with PAF (18% of all patients with PAF). Univariate analysis showed that young age (< 40 years; odds ratio [OR] 4.9; 95% confidence interval [CI] 1.0-23.6), abdominal pains (OR 4.8; 95% CI 1.2-19.1), rectal bleeding (OR 4.3; 95% CI 1.2-15.6), fatigue (OR 3.9; 95% CI 1.1-14.4), multiple external (OR 6.0; 95% CI 1.5-24.6)/internal fistula openings (OR 61.2; 95% CI 9.8-383.4), fissures (OR 4.4; 95% CI 1.1-17.2), and proctitis (OR 22.9; 95% CI 1.9-277.5) increased the likelihood of having CD. CONCLUSION: With FCP-based screening for CD, approximately one in six patients with PAF, and even one in three patients with PAF < 40 years were diagnosed with CD. Therefore, FCP measurement is suggested in all patients with PAF, especially when they are < 40 years.