To compare categories for activity/severity according to the Disease Activity Score 28-joint count (DAS28), the Clinical Disease Activity Index (CDAI), and the Routine Assessment of Patient Index Data 3 (RAPID3), an index without formal joint counts calculated in 5 versus >100 seconds, as well as the European League Against Rheumatism (EULAR)- DAS28 and the RAPID3 response criteria, in the Rheumatoid Arthritis Prevention of Structural Damage (RAPID 1) clinical trial of certolizumab pegol (CZP).
Post hoc analyses were performed using correlations, cross-tabulations, and kappa statistics. Patients (treated with CZP plus methotrexate [MTX] or placebo plus MTX) were classified at baseline and at 52 weeks as high, moderate, low activity/severity or remission, according to the DAS28 (>5.1, >3.2 to ≤5.1, 2.6 to ≤3.2, <2.6 [total range 0-10]), the CDAI (>22, >10 to ≤22, >2.8 to ≤10, ≤2.8 [total range 0-76]), and RAPID3 (>12, >6 to ≤12, >3 to ≤6, ≤3 [total range 0-30]), as well as for good, moderate, and poor EULAR-DAS28 and proposed RAPID3 response criteria.
All measures were correlated significantly: RAPID3 with DAS28 and CDAI (rho > 0.7), higher than erythrocyte sedimentation rate with C-reactive protein level (rho = 0.47). At 52 weeks, DAS28, CDAI, and RAPID3 low activity/remission was seen in 30%, 44%, and 42% of CZP-treated patients versus 3%, 7%, and 10% of control patients. Good, moderate, and poor EULAR-DAS28 responses were seen in 30%, 51%, and 19% of CZP-treated patients versus 3%, 28%, and 70% of control patients, and for RAPID3 in 39%, 30%, and 32% of CZP-treated patients versus 8%, 16%, and 76% of control patients. Kappa and weighted kappa values ranged from 0.36-0.53, indicating fair to moderate agreement.
RAPID3, DAS28, and CDAI give similar results to distinguish CZP patients from controls in the RAPID 1 clinical trial. DAS28 is specific for clinical trials; RAPID3 appears pragmatically useful for usual care.