Objective: To determine the validity, reliability and responsiveness of the Work Productivity and Activity Impairment questionnaire in AS (WPAI:SpA).
Methods: Baseline and Week-24 data from a randomized, double-blind study of adalimumab in patients with AS were used. Discriminative validity of WPAI:SpA absenteeism, presenteeism, overall work productivity loss and activity impairment scores was assessed relative to patient-reported outcomes: Bath AS Disease Activity Index (BASDAI), AS Quality of Life Questionnaire (ASQOL), Short-Form 36 Health Survey (SF-36), Physical and Mental Component Summaries (PCS and MCS, respectively) and Health Utilities Index Mark 3 (HUI-3). Responsiveness of the WPAI:SpA instrument was assessed for patients meeting the minimum clinically important differences (MCIDs) for ASQOL and BASDAI (i.e. quality of life and clinical responders, respectively) and quantified with standardized response mean (SRM) calculations.
Results: Of 315 patients, 205 were employed at baseline. Patients with more severe AS (BASDAI > median) showed significantly greater impairment in work and daily activities than patients with lesser disease severity (P < 0.001). This trend was consistent for ASQOL, SF-36 PCS, SF-36 MCS and HUI-3. There were significant differences in WPAI:SpA scores for patients achieving BASDAI clinical response and ASQOL quality of life response vs non-responders. For responders, SRMs were large for work presenteeism, overall work impairment and activity impairment (-0.86 to -1.29 for BASDAI; -0.89 to -1.18 for ASQOL) and small for absenteeism (-0.25 for BASDAI; -0.31 for ASQOL).
Conclusions: The WPAI:SpA is a valid, reliable and responsive tool for assessing work productivity for patients with AS.
Trial registration: ClinicalTrials.gov, http://clinicaltrials.gov/ct2/home, NCT00085644.