Cross-cultural validation of a disease-specific patient-reported outcome measure for systemic lupus erythematosus in Canada.

Objective: The LupusPRO, a disease-targeted patient-reported outcome measure, was developed and validated in US patients with systemic lupus erythematosus (SLE). We report the results of the cross-cultural validation study of the English version of the LupusPRO among patients in Canada with SLE.
Method: The LupusPRO was administered to English-speaking Canadian patients with SLE. Demographic, clinical, and serological characteristics were obtained, and the Medical Outcomes Study Short Form-36 (SF-36) and LupusPRO were administered. Disease activity was ascertained using the Safety of Estrogens in Lupus Erythematosus National Assessment-Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI) and the Lupus Foundation of America definition of flare (Yes/No). Damage was assessed using the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI). Physician disease activity and damage assessments were also ascertained using visual analog scales. A mail-back LupusPRO form was completed within 2-3 days of the index visit. Items tested were internal consistency reliability (ICR), test-retest reliability (TRT), convergent and discriminant validity (against corresponding domains of the SF-36), criterion validity (against disease activity or health status), and known-groups validity.
Results: Participants were 123 Canadian patients with SLE (94% women); mean age was 47.7 (SD 14.8) years. The median (interquartile range) SELENA-SLEDAI and SDI were 4 (6) and 1 (3), respectively. The ICR of the LupusPRO domains ranged from 0.60 to 0.93, while the TRT range was 0.62-0.95. Measures observed were convergent and discriminant validity with corresponding domains of SF-36, criterion validity, and known-groups validity against disease activity, damage, and health status. Confirmatory factor analysis showed a good fit.
Conclusion: The LupusPRO has fair psychometric properties among Canadian patients with SLE, and prospective studies to establish minimally important difference are continuing.