Validity of single variables and indices to measure disease activity in rheumatoid arthritis.

We compared the sensitivity of several variables in 2 trials between second-line agents in our clinic. In a trial comparing sulfasalazine with hydroxychloroquine significant differences were found in favor of sulfasalazine by the Ritchie score, number of swollen joints, disease activity score (DAS), physical disability and radiographic damage. This could not be determined by number of tender joints, patient's global assessment, pain, morning stiffness, or erythrocyte sedimentation rate (ESR). In a trial comparing methotrexate with azathioprine significant differences could be found in favor of methotrexate by the variables of pain, DAS, ESR, C-reactive protein, hemoglobin and thrombocytes; not by Ritchie score, number of tender joints and number of swollen joints. Combining the results of the various validation procedures leads to relative quality of the variables.