Validation of the German Inflammatory Bowel Disease Activity Index (GIBDI): An Instrument for Patient-Based Disease Activity Assessment in Crohn's Disease and Ulcerative Colitis

Introduction Assessment of disease activity in Crohn's disease (CD) and ulcerative colitis (UC) is usually based on the physician's evaluation of clinical symptoms, endoscopic findings, and biomarker analysis. The German Inflammatory Bowel Disease Activity Index for CD (GIBDI _CD) and UC (GIBDI _UC) uses data from patient-reported questionnaires. It is unclear to what extent the GIBDI agrees with the physicians' documented activity indices. Methods Data from 2 studies were reanalyzed. In both, gastroenterologists had documented disease activity in UC with the partial Mayo Score (pMS) and in CD with the Harvey Bradshaw Index (HBI). Patient-completed GIBDI questionnaires had also been assessed. The analysis sample consisted of 151 UC and 150 CD patients. Kappa coefficients were determined as agreement measurements. Results Rank correlations were 0.56 (pMS, GIBDI _UC) and 0.57 (HBI, GIBDI _CD), with p<0.001. The absolute agreement for 2 categories of disease activity (remission yes/no) was 74.2% (UC) and 76.6% (CD), and for 4 categories (none/mild/moderate/severe) 60.3% (UC) and 61.9% (CD). The kappa values ranged between 0.47 for UC (2 categories) and 0.58 for CD (4 categories). Discussion There is satisfactory agreement of GIBDI with the physician-documented disease activity indices. GIBDI can be used in health care research without access to assessments of medical practitioners. In clinical practice, the index offers a supplementary source of information.