From Stool to Scope: Optimising FIT Thresholds to Guide Future Panenteric Capsule Endoscopy and Reduce Colonoscopy...

Area of Science:

• Gastroenterology
• Diagnostic Imaging
• Health Economics

Background:

• Panenteric capsule endoscopy (PCE) is a non-invasive tool for diagnosing iron deficiency anaemia (IDA).
• High conversion rates to conventional colonoscopy (CCC) after PCE reduce cost-effectiveness and patient satisfaction.
• Optimizing the faecal immunochemical test (FIT) threshold may improve patient selection for PCE in IDA.

Purpose of the Study:

• To assess the predictive value of FIT for colorectal cancer (CRC), polyp burden, and CCC in IDA patients.
• To identify an optimal FIT threshold for stratifying IDA patients and reducing unnecessary colonoscopies.
• To evaluate the cost-effectiveness of different FIT thresholds in the IDA diagnostic pathway.

Main Methods:

• Multicentre, retrospective observational study (CLEAR IDA) of 1531 patients referred via the two-week-wait pathway.
• Analysis of colonoscopy findings and extrapolation using NHS England's PCE-to-colonoscopy referral criteria.
• Receiver operating characteristic (ROC) curve analysis, decision curve analysis, and cost-benefit modelling to determine optimal FIT threshold.

Main Results:

• FIT demonstrated diagnostic accuracy (AUC) of 0.78 for CRC, 0.58 for polyps, and 0.69 for CCC.
• FIT = 15 µg/g was the lowest threshold associated with significantly increased CCC rates (p=0.02).
• Optimal cost-effective FIT threshold range identified between 10-17.6 µg/g, balancing diagnostic yield and resource utilization.

Conclusions:

• FIT is an imperfect triage tool for IDA patients but optimizing thresholds can enhance cost-effectiveness.
• An optimal FIT threshold range of 10-17 µg/g may guide appropriate PCE use and reduce unnecessary CCC.
• Threshold selection should be tailored to local healthcare service capacity and resource availability.