Can health utility measures be used in lupus research? A comparative validation and reliability study of 4 utility indices

Objective. To assess validity and reliability of 4 utility indices in patie nts with systemic lupus erythematosus (SLE). Methods. Twenty-five patients with stable SLE underwent assessment of disea se activity [Systemic Lupus Disease Activity Measure (SLAM-R) and SLE Disea se Activity Index (SLEDAI)] and damage [Systemic Lupus Collaborating Clinic s/American College of Rheumatology Damage Index (SLICC/ACR DI)] and complet ed a health survey [Medical Outcome Survey Short Form-36 (SF36)] and 4 util ity measures: the visual analog scale (VAS), the time trade-off (TTO), the standard gamble (SG), and the McMaster Health Utilities Index Mark 2 (HUI2) . To assess validity, Pearson's correlations were calculated between the SF -36 subscales and the utility measures. To assess reliability, intraclass c orrelations or kappa coefficients were calculated between first and second assessments, performed from 2 to 4 weeks apart, in patients without importa nt clinical change in disease activity. Results. Disease activity from a SLAM-R varied from 0 to 14 (median = 4) an d SLEDAI from O to 18 (median = 0). All subscales of the SF-36 correlated w ell with the VAS [lowest r = 0.56, 95% confidence interval (CI) (0.17, 0.80 )] and poorly with the SG [maximum r = 0.41, CI (-0.01, 0.70); minimum r = 0.10, CI (-0.32, 0.50)]. The subscales of bodily pain (r = 0.56), mental he alth (r = 0.45), physical functioning (r = 0.62), role-emotional (r = 0.47) , social functioning (r = 0.49) and vitality (r = 0.44) correlated signific antly with TTO. All subscales correlated significantly [lowest r = 0.48, CI (0.09, 0.75)] with the HUI2 index of pain. Intraclass correlations for the VAS (ICC = 0.67) and TTO (ICC = 0.60) were good. They were fair for the SG (ICC = 0.45). The kappa coefficient was poor (0.32) for the HUI attribute of pain, but varied from fair (0.46) to excellent (0.88) for the remaining attributes. Regression analysis showed that a model incorporating the SLAM- R value and SF-36 subset of mental health was a good predictor of VAS and T TO utility measures. Conclusion. The VAS, TTO, and to some extent, the HU12, when compared with the SF-36 health survey, are valid and reliable measures to assess health r elated quality of life in a group of patients with SLE and may be useful fo r future research in this population. On the basis of these results the use fulness of the SG is questionable in these patients.