Estimating EQ-5D and OAB-5D health state utilities for patients with overactive bladder

BACKGROUND Limited utility data on patients suffering from overactive bladder (OAB) are available in the literature. The objectives of this study were to estimate utility values in patients with OAB using the generic EQ-5D questionnaire and the OAB-5D disease specific questionnaire, to investigate the relationship between utilities and symptoms, and to evaluate the sensitivity of the two instruments to changes in symptom severity. METHODS Analyses were based on pooled data from three large multicenter randomized 12-week placebo-controlled trials (SCORPIO, ARIES, CAPRICORN). Patients completed a micturition diary, EQ-5D and OAB-q (a quality of life questionnaire from which OAB-5D is derived) at baseline and at weeks 4, 8 and 12. Time trade-off tariffs elicited from UK population were applied to obtain utilities from both instruments. Repeated measures regressions were used to estimate EQ-5D and OAB-5D utilities by micturition frequency and incontinence severity level. As a test of sensitivity of the instruments, utility changes from baseline to week 12 were estimated by symptomatic response (improvement, stable or worsening). RESULTS The sample included 4427 patients. Mean utilities (± standard deviation) across all visits were 0.82 (± 0.21) for EQ-5D and 0.86 (±0.09) for OAB-5D. Correlation between EQ-5D and OAB-5D was 0.34 (p < 0.0001). Both OAB-5D and EQ-5D utilities increased as OAB symptoms improved. Utility values were similar for severe levels of symptoms, but higher with OAB-5D than with EQ-5D for mild cases. Micturitions and incontinence had similar impact on EQ-5D utilities, but micturitions had greater impact on OAB-5D utilities than incontinence. Changes from baseline in OAB-5D utilities differed significantly according to symptomatic response. Changes in EQ-5D utilities were not significantly associated with changes in micturition frequency and weakly associated with changes in incontinence severity among patients with mild symptoms at baseline. CONCLUSIONS This study showed that both EQ-5D and OAB-5D can detect changes in severity of OAB, especially in severe cases. However, OAB-5D is more sensitive than EQ-5D in measuring differences between treatments in milder cases. Both OAB-5D and EQ-5D-although leading to different results-may be useful to derive utilities from clinical trial data and perform cost-effectiveness analyses. TRIAL REGISTRATION Clinical Trials NCT00689104, NCT00662909, NCT00912964.