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 patients with systemic lupus erythematosus (SLE).

METHODS: Twenty-five patients with stable SLE underwent assessment of disease activity [Systemic Lupus Disease Activity Measure (SLAM-R) and SLE Disease Activity Index (SLEDAI)] and damage [Systemic Lupus Collaborating Clinics/American College of Rheumatology Damage Index (SLICC/ACR DI)] and completed a health survey [Medical Outcome Survey Short Form-36 (SF-36)] and 4 utility 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 correlations or kappa coefficients were calculated between first and second assessments, performed from 2 to 4 weeks apart, in patients without important clinical change in disease activity.

RESULTS: Disease activity from a SLAM-R varied from 0 to 14 (median = 4) and SLEDAI from 0 to 18 (median = 0). All subscales of the SF-36 correlated well 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 health (r = 0.45), physical functioning (r = 0.62), role-emotional (r = 0.47), social functioning (r = 0.49) and vitality (r = 0.44) correlated significantly 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 TTO utility measures.

CONCLUSION: The VAS, TTO, and to some extent, the HUI2, when compared with the SF-36 health survey, are valid and reliable measures to assess health related quality of life in a group of patients with SLE and may be useful for future research in this population. On the basis of these results the usefulness of the SG is questionable in these patients.