P0342 Quantitative faecal immunochemical test (qFIT) is comparable to calprotectin as a biomarker of IBD: Prospective longitudinal analysis of disease activity and endoscopic mucosal healing
Authors: Cartlidge P , Le-Saint Grant A , Siu-Ying Lau P , Hodge M , Hall R , Strachan J , Chuah S , Whelan R , Ong S , Brownson E , Campbell I , Poulose B , Oddy A , MacDonald J , Seenan J P , Gaya D , Mowat C , Ho G T 
Published: January 2025

Abstract

Background
Quantitative faecal immunochemical test (qFIT) to detect stool haemoglobin is used for colorectal cancer screening at a population level in UK (& Europe) with high patient acceptability due to its ease of use and relative low cost . We evaluate the clinical utility of qFIT with faecal calprotectin (fCal) in IBD.

Methods
UC and CD patients from the prospective, multi-centre longitudinal MUSIC study (2020-2024; www.musicstudy.uk) were included. qFIT and fCal samples were collected every three months at five time points. qFIT analysis was conducted using the HM-JACKarc automated analyser. Blinded qFIT results were compared with physician global assessment, clinical indices (HBI, SCCAI)*, and endoscopic findings. All patients had active disease at baseline, with a repeat colonoscopy at timepoint 3 to assess for complete mucosal healing (CMH), defined as Mayo-score or SES-CD of 0 in UC and CD respectively.

Results
357 qFIT results were analysed from 124 patients (58 colonic CD/ 66 UC). qFIT was significantly higher in active disease compared to remission (n=227 vs. 130; 100µgHb/g vs 2.5 µgHb/g; p&lt;0.001). The ability of qFIT to predict active disease was higher in those with UC than colonic CD AUC 0.77 and 0.69 respectively (in 179 UC /178 CD samples). Optimal threshold for predicting remission was &lt;14µgHb/g, with a sensitivity of 0.73, specificity of 0.66. 27 qFIT results from ileal CD patients showed no significant difference between active disease and remission (p=0.2). 339 qFIT results had paired FCal results. The ability of fCal to predict active disease was higher in UC than colonic CD with AUC of 0.82 and 0.77 respectively. For both IBD types, the AUC was 0.81 [Figure 1]. The optimal fCal level was 240 µg/g for remission, with a sensitivity of 0.76 and specificity of 0.72. Combining qFIT and fCal improved prediction of remission to an AUC of 0.82. qFIT performed better than fCal at predicting mucosal inflammation with an AUC 0.74 vs. 0.67 respectively. In 76 UC patients, Mayo endoscopy scores were paired with mean qFIT levels, showing a correlation: score 0 = 32 µgHb/g, score 1 = 181 µgHb/g, score 2 = 217 µgHb/g, and score 3 = 295 µgHb/g (one-way ANOVA, p = &lt;0.001). 20 patients (from 52) achieving CMH, showed significant reduction in qFIT using paired T-test (107 vs 37 µgHb/g, p=0.026). In the 32 patients with ongoing inflammation, qFIT remained high (213 vs. 170 µgHb/g, p=0.23).

Conclusion
qFIT is comparable to fCal as a biomarker of IBD activity. With its superior patient acceptability and intrinsic test qualities, it should be considered as routine clinical test in IBD. Further large scale validation is warranted to establish its clinical utility.

References
*AUC – Area Under Curve **HBI-Harvey Bradshaw Index ***SCCAI – Simple Colitis Activity Index