Variables related to utility in patients with ankylosing spondylitis

The objective of this study was to identify variables associated to the utility of the health states in patients with ankylosing spondylitis (AS). A cross-sectional study was performed in a tertiary care centre. AS patients (New York modified criteria) were included. Demographic and disease-related variables were collected. The social tariffs of the EuroQol-5D (EQ-5D) were used to obtain utility values. Univariate and multivariate regression analyses were used in order to identify variables associated with utility. Seventy patients, 52 male (74.3%), with age (mean +/- SD) 43.7 +/- 9.1 years and disease duration 10.8 +/- 8.1 years, were included. The mean utility was 0.5625 +/- 0.3364. In the univariate analysis, patient global assessment, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Bath Ankylosing Spondylitis Functional Index (BASFI) had a good correlation with the EQ-5D values (Pearson's product moment correlation coefficient r > 0.6) whereas physician global assessment, patient pain assessment, and cervical rotation had a moderate correlation with the EQ-5D (0.6 > r > 0.4). Patients with significant comorbidity had lower utility values (0.3563 +/- 0.068) than those without it (0.6796 +/- 0.041, p = 0.0001). In the multivariate analysis, BASFI and BASDAI kept an independent association with utility and they explained a 62% of the variance of the utility values. In this study, physical function and disease activity, two outcomes with good responsiveness to the treatment, were the main determinants of the utility of the health states in AS patients.