To develop and validate a modified version of the Disease Activity Score with 28 joint count (mDAS28), for use in epidemiological research, when acute-phase reactant values are unavailable.
In a cross-sectional development cohort (5729 patients), statistically significant predictors of the logarithm of erythrocyte sedimentation rate (lnESR) were identified. After computation of the mDAS28, a cross-sectional validation cohort (5578 patients) was used to evaluate internal, criterion, and construct validities. The ability of the mDAS28 to discriminate between disease states was also assessed. A second validation cohort (longitudinal, 336 pairs of patient visits) was used to assess sensitivity to change.
Significant predictors of lnESR included tender and swollen joints with 28 counts, patient's and physician's assessments of global health, and patient's assessment of pain (visual analog scale 0-100 mm) and a physical function (modified Health Assessment Questionnaire 0-3; mHAQ). Satisfactory internal validity (alpha = 0.72) and strong criterion validity compared to the DAS28, the Simplified Disease Activity Index (SDAI), and the Clinical Disease Activity Index (CDAI) (r = 0.87-0.96) were found. Predictive validity was demonstrated by good correlation with the mHAQ (r = 0.58). The mDAS28 showed substantial agreement with the DAS28, SDAI, and CDAI in discriminating between disease states (kappa = 0.70-0.77) and moderate to substantial agreement between response levels (kappa = 0.52-0.73). Both mDAS28 and DAS28 measures classified patients similarly in remission compared to the SDAI and CDAI. The mDAS28 was superior in detecting change (standardized response mean = 0.58) followed by the DAS28, CDAI, and SDAI.
The mDAS28 is a valid and sensitive tool to assess disease activity in epidemiological research, as an alternative to the DAS28, when acute-phase reactant values are unavailable.