Psychometric properties of MDHAQ/RAPID3 in patients with systemic lupus erythematosus

{Background: The Multidimensional Health Assessment Questionnaire (MDHAQ) is a patient-reported outcome (PRO) tool that includes the Routine Assessment of Patient Index Data 3 (RAPID3), an index that can be calculated at the point of care. The objective of this study was to perform psychometric analyses of MDHAQ/RAPID3 to study its measurement properties in systemic lupus erythematosus (SLE). Methods: The MDHAQ was completed by 161 SLE patients in routine care, along with LupusPRO (a disease-specific PRO). The SLE disease-specific activity index (SELENA-SLEDAI) and damage (SDI) were assessed. Data from 70 patients with rheumatoid arthritis who had completed MDHAQ during their routine medical care were used as controls to compare the results of Physical Function (FN) domain exploratory factor analysis. Internal consistency reliability (ICR) for FN items was calculated using Cronbach's . Validity of MDHAQ/RAPID3 was evaluated for content validity and construct validity. Responsiveness of the RAPID3 to changes in disease activity anchors was assessed. Results: The ICR of the 10 physical function items on Cronbach's alpha was 0.88. Exploratory factor analysis revealed cross-loadings of three FN items. RAPID3 showed a strong correlation with LupusPRO health-related quality of life score (rho-0.68 (p<0.001)), indicating convergent validity. RAPID3 scores did not correlate with disease activity indices or SDI. After adjustment for fibromyalgia status, a weak correlation with the Physician's Global Assessment (PGA) (rho=0.31