Development and investigation of a non-invasive disease severity index for inflammatory bowel disease.

Introduction: The disease severity index (DSI) encapsulates the inflammatory bowel disease (IBD) burden but requires endoscopic investigations. This study developed a non-invasive DSI using faecal calprotectin (DSI-fCal) and faecal myeloperoxidase (DSI-fMPO) instead of colonoscopy.

Methods: Adults with IBD were recruited prospectively. Baseline biomarker concentrations were used to develop DSI-fCal and DSI-fMPO, and these were correlated with the original DSI, IBD-symptoms, endoscopic activity, and quality-of-life (QoL). Area under the receiver-operating-characteristics curves (AUROC) assessed DSI-fCal/DSI-fMPO as predictors of clinical and biochemical remission at six months (symptom remission and fCal <150 μg/g, respectively), and a complicated IBD-course at 24 months (disease relapse needing escalation of biologicals/immunomodulators/recurrent corticosteroids, IBD-hospitalisations/surgeries). Multivariable logistic regression assessed the utility of DSI-fCal/DSI-fMPO in predicting a complicated IBD-course at 24 months.

Results: In total, 171 patients were included (Crohn's disease=99, female=90, median age=46y (IQR 36-59)). DSI-fCal and DSI-fMPO correlated with the original DSI (r>0.9, p<0.001), endoscopic indices (r=0.45-0.49, p<0.001), IBD-symptoms (r=0.53-0.58, p<0.001) and QoL (r=-0.57-0.58, p<0.001). Baseline DSI-fCal (AUROC=0.79, 95% CI 0.65-0.92) and DSI-fMPO (AUROC=0.80, 95% CI 0.67-0.93) were associated with 6-month clinical and biochemical remission. DSI-fCal (AUROC=0.83, 95% CI 0.77-0.89) and DSI-fMPO (AUROC=0.80, 95% CI 0.73-0.87) performed similarly in predicting a complicated IBD-course to the original DSI (pdifference>0.05). The non-invasive DSI was independently associated with a complicated IBD-course on multivariable analyses (DSI-fCal28, aOR=6.04, 95% CI 2.42-15.08; DSI-fMPO25, aOR=7.84, 95% CI 2.96-20.73).

Conclusions: The DSI-fCal and DSI-fMPO perform similarly in prognosticating the longitudinal disease course as the original DSI, whilst avoiding a need for an endoscopic assessment.