Development and validation of a patient-based disease activity score in rheumatoid arthritis that can be used in clinical trials and routine practice

Objective: Assessor-based disease activity measures such as the Disease Activity Score in 28 joints (DAS28), although widely used in rheumatoid arthritis (RA), have high interobserver variability. We developed and validated a patient-based disease activity score (PDAS) as an alternative assessment. Methods: Patients' assessments of swollen or tender joints, visual analog scales for pain and general health, the Health Assessment Questionnaire, and erythrocyte sedimentation rate (ESR) were used to develop the PDAS. In a developmental cohort (204 patients), regression analyses determined the best fit with the DAS28. A validation cohort (322 patients) subsequently evaluated criterion and construct validity against a range of outcome measures, including the Nottingham Health Profile (NHP) and Short Form 36 (SF-36). Sensitivity to change was assessed in 56 patients after 6 months of treatment with disease-modifying antirheumatic drugs or biologics. Results: In the developmental cohort, the PDAS with ESR (PDAS1) and without ESR (PDAS2) achieved excellent fit with the DAS28 (r = 0.88 and 0.74, respectively). In the validation cohort, the PDAS showed high criterion validity by correlation with the DAS28 (PDAS1: r = 0.89, PDAS2: r = 0.76). Construct validity was demonstrated by high correlations with a range of disease activity measures (r ≥ 0.45), whereas low correlations (r < 0.45) with mental and social components of the SF-36 and NHP indicated divergent validity. The PDAS and DAS28 had similar sensitivity to change, determined using effect sizes (DAS28 = 1.03, PDAS1 = 1.02, PDAS2 = 0.77) or standardized response means (DAS28 = 0.79, PDAS1 = 0.77, PDAS2 = 0.73). Conclusion: The PDAS1 and PDAS2 are valid and sensitive tools to assess disease activity in RA. They appear suitable for clinical decision making, epidemiologic research, and clinical trials