Objective: To assess the psychometric properties of the Health Assessment Questionnaire (HAQ) disability index (DI) in patients with gout.
Methods: This study was conducted in a multicenter cohort of patients with gout whose data were collected at baseline (time 0) and 6 months later (time 6). Reliability was assessed by test-retest reliability (intraclass correlation coefficient [ICC]) and internal consistency (Cronbach's alpha coefficient). Construct validity was assessed with convergent validity (HAQ DI correlation with Short Form 36 [SF-36]) and discriminative validity (HAQ DI correlation with clinical features). Sensitivity to change was determined by comparing HAQ DI time 0 versus HAQ DI time 6 (percentage of change, effect size, smallest real difference [SRD], and Guyatt's responsiveness index [GRI]).
Results: We included 206 patients (96.6% men, mean +/- SD age and disease duration 56.3 +/- 12.4 years and 9.3 +/- 8.5 years, respectively). Of these, 52.4% had joint pain, 22.8% swelling, 32.5% reduced joint mobility, and 36.9% tophi. The mean HAQ DI score was 0.59 +/- 0.77 (95% confidence interval [95% CI] 0.49-0.70). ICC (n = 36, evaluations at baseline and 5 days later) was 0.76. Cronbach's alphas were 0.91 (95% CI 0.88-0.92, P = 0.000) for the 20 HAQ DI items and 0.93 (95% CI 0.92-0.94, P = 0.000) for the 8 HAQ DI categories. The HAQ DI correlated in predictable ways with SF-36 subscales and clinical variables, and discriminated between subgroups with and without any joint pain, swelling, and tophi. Concerning sensitivity to change (n = 167), the difference between HAQ DI time 0 and HAQ DI time 6 was 0.31 +/- 0.58 (effect size 0.62, SRD 0.59, and GRI 1.91). DeltaHAQ DI correlated with Deltapain (r = 0.349, P = 0.000).
Conclusion: The HAQ DI is a valid and reliable measure of functioning in patients with gout.