PG125 ESTABLISHING THE RELATIONSHIP BETWEENTHE ULCERATIVE COLITIS DISEASE ACTIVITY INSTRUMENT (UCDAI) AND PATIENT HEALTH RELATED QUALITY OF LIFE FROM A LARGE RANDOMISED CONTROLLED TRIAL

Abstract

OBJECTIVES: The purpose of this study was to conduct a statistical mapping between standard assessments of disease severity in ulcerative colitis (UC) using the ulcerative colitis disease activity index (UCDAI) and a patient reported generic health-related utility instrument to estimate patient preference-based health utility. METHODS: Multinomial logistic regression was used to estimate response probabilities to each of the five domains of the EuroQol-5D index instrument (EQ-5D) from assessments of UC severity using the original UCDAI and an abbreviated (ie. No endoscopy) UCDAI instrument in patients enrolled into a clinical trial studying the use of oral/rectal mesalazine combination maintenance therapy. Predicted EQ-5D health utility was estimated by Monte Carlo bootstrap simulation. The predictive ability of the response mapping was assessed by comparing estimated and directly measured utility derived from the UK tariff (Dolan, 1997). RESULTS: Evaluable datawere available for 128 patients,59%of whom were male, and for which the median age at screening was 43.5 years (IQR 30 to 54). Using UCDAI item responses as predictor variables, the percentage of variance in domain response attributable to predictor variable change ranged from 20.4% (ANXIETY/DEPRESSION) to 42.5.5% (SELF CARE). Summary UCDAI score was a less effective predictor of the same domains (R2 = 13.2% and 20.4 respectively). Items from the abbreviated UCDAI (no endoscopy score) showed comparable explanatory performance (R2 range 21.3% to 38.0%). The mean utility predicted by the UCDAI item algorithm was 0.844 (sd 0.104) and 0.852 (sd 0.175) by estimation directly from EQ-5D responses (p = 0.238). The mean squared error (MSE) between the actual and predicted utilities was 0.019. Predicted EQ-5D utility was within 3% of the actual utility in 38.1% of cases and within 10% of the actual utility in 58.5% of cases. CONCLUSIONS: In this study responsemapping of UC disease activity to EQ-5D domains produced reliable estimates of preference-based health-related utility. The near-identical explanatory power of models using either the original or abbreviated UCDAI assessment suggests that endoscopy adds little information to patient perception of UC disease severity. The results from this study will enable future investigators to generate health-related utility from the UCDAI in trials where this data was not prospectively collected