Validation of the Inflammatory Bowel Disease Disability Index in a population-based cohort

Background IBDs are chronic destructive disorders that negatively affect the functional status of patients. Recently, the Inflammatory Bowel Disease Disability Index (IBD-DI) was developed according to standard WHO processes. The aims of the current study were to validate the IBD-DI in an independent patient cohort, to develop an index-specific scoring system and to describe the disability status of a well-defined population-based cohort of French patients with IBD. Methods From February 2012 to March 2014, the IBD-DI questionnaire was administered to a random sample of adult patients with an established diagnosis of IBD issued from a French population-based registry. The IBD-DI consists of 28 items that evaluate the four domains of body functions, activity participation, body structures and environmental factors. Validation included item reduction and data structure, construct validity, internal consistency, interobserver and intraobserver reliability evaluations. Results 150 patients with Crohn's disease (CD) and 50 patients with UC completed the IBD-DI validation phase. The intraclass correlation coefficient for interobserver reliability was 0.91 and 0.54 for intraobserver reliability. Cronbach's alpha of internal consistency was 0.86. IBD-DI scores varied from 0 to 100 with a mean of 35.3 (Q1=19.6; Q3=51.8). IBD-DI scores were highly correlated with Inflammatory Bowel Disease Questionnaire (-0.82; p<0.001) and SF-36 (-0.61; p<0.05) scores. Female gender (p<0.001), clinical disease activity (p<0.0001) and disease duration (p=0.02) were associated with higher IBD-DI scores. Conclusions The IBD-DI has been validated for use in clinical trials and epidemiological studies. The IBD-DI showed high internal consistency, interobserver reliability and construct validity, and a moderate intraobserver reliability. It comprises 14 questions and ranges from 0 to 100. The mean IBD-DI score was 35.3 and was associated with gender, clinical disease activity and disease duration. Further research is needed to confirm the structural validity and to assess the responsiveness of IBD-DI.