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.