Diagnostic Accuracy of the Faecal Immunochemical Test in Triage of Symptomatic Patients Referred for Colonoscopy: A Prospective Single-Centre Study.

Abstract

Aim: The faecal immunochemical test (FIT) is endorsed by NICE for triaging symptomatic patients referred from primary care. This prospective diagnostic accuracy study assessed the performance of FIT in detecting significant colorectal pathology among symptomatic patients referred for colonoscopy in secondary care. Method: Between May 2023 and May 2024, FIT kits were distributed to 1296 adult patients referred for lower gastrointestinal (GI) endoscopy. A FIT threshold of ≥ 50 ng/mL prompted urgent colonoscopy; values < 50 ng/mL led to outpatient assessment unless Health Service Executive Priority 1 criteria were met. A complete colonoscopy served as the reference standard. Results: A total of 1113 patients (86%) returned valid FIT results; 215 (19%) were FIT positive. FIT-positive patients were significantly older than FIT-negative patients (58 vs. 54 years, p < 0.01). Among FIT-positive patients, 177 (82%) underwent colonoscopy, compared with 139 (15%) of FIT-negative patients. Colorectal cancer was detected in 20 FIT-positive patients and in none of the FIT-negative group, yielding a sensitivity and negative predictive value (NPV) of 100% (95% CI for sensitivity: 83-100 and NPV: 97-100). The area under the receiver operating characteristic (ROC) curve was 0.868 (95% CI: 0.82-0.91). For advanced polyps and inflammatory pathology, sensitivities were 77% and 89%, with NPVs of 98% for both. The mean time to endoscopy was shorter in FIT-positive patients (7 vs. 21 weeks, p < 0.01). Conclusion: FIT demonstrates excellent sensitivity for colorectal cancer and may serve as a safe, effective triage tool in symptomatic patients, helping optimise endoscopy services in resource-limited settings.