Development and validation of a new disease severity index: The inflammatory bowel disease index

Objective: To develop, validate and apply a generic clinical severity index applicable to all adult patients with IBD.Design: A review of the literature and an expert focus group consultation were carried out in order to draw out relevant items. The new index was called the inflammatory bowel disease index (IBDex). Standard psychometric analysis was carried out. The construct validity was assessed against biochemical markers, clinical and endoscopic indices. The new index was completed again within 6 weeks in to check responsiveness and reproducibility.Results: IBDex was used to assess 255 IBD adult patients (125 with Crohn's disease and 130 with ulcerative colitis), and 64 patients were re-evaluated within 6 weeks. It had good internal consistency (Cronbach alpha = 0.79) and correlated very well with Harvey Bradshaw index (r = 0.94), the simple clinical colitis activity index (r = 0.92) , the Mayo clinic index (r = 0.87 ) and the simple endoscopic score (r = 0.76) all with p values less 0.05. IBDex had a moderate but positive correlation with C reactive protein (r = 0.51) and erythrocyte sedimentation rate (r = 0.36) p values both less than 0.05. The test-retest reliability was good (intra-class correlation coefficient 0.97) and responsiveness ratio was 2.27.Conclusion: IBDex is the first properly validated clinical disease severity index in IBD. Our results showed that it is valid, reliable and reproducible and has the potential to be used in clinical practice.