Background and aim: Recently, the Inflammatory Bowel Disease-Disability Index (IBD-DI) was developed to assess disability in inflammatory bowel disease (IBD). Our aim was to validate the Portuguese version of IBD-DI according to the COnsensus-based Standards for the selection of the health Measurement INstruments (COSMIN) recommendations.
Materials and methods: After translation into Portuguese, the IBD-DI was administered by two interviewers to IBD patients at baseline and after 4 weeks and 4 months. We evaluated reliability (internal consistency, test-retest, and inter-rater reliability and measurement error), construct validity, responsiveness, and interpretability.
Results: At baseline, 129 patients (73=Crohn's disease; 56=ulcerative colitis) completed the IBD-DI. After 4 weeks and 4 months, 118 and 89 patients repeated the questionnaire, respectively. Factor analysis confirmed the unidimensionality of the scale and reduced the final version to 14 items. The Cronbach's α was 0.88. The intraclass correlation coefficients were 0.87 and 0.99 for test-retest (baseline and 4 weeks) and inter-rater reliability, respectively. The smallest detectable change was 18.64 at the individual level and 1.87 at the group level. IBD-DI scores correlated negatively with the total, physical, and mental scores of Short Form-36 items. The change score of IBD-DI between baseline and 4 months correlated negatively with the clinical evolution of patients. The minimal important change was 16.96. IBD-DI scores ranged from 0 to 78.6, with a mean of 21.8±18.1. Female sex, professional inactivity, and clinical disease activity were associated with higher IBD-DI scores.
Conclusion: The Portuguese version of IBD-DI obtained is a reliable, valid, responsive, and interpretable (at the group level) tool to assess disability in Portuguese IBD patients.