Plasma viscosity--a new appraisal of its use as an index of disease activity in rheumatoid arthritis.

The suitability of the plasma viscosity (PV) test has been examined in relation to the more commonly used erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) estimations as a diagnostic aid in 120 outpatients with rheumatoid arthritis (RA) and as an index of improvement during subsequent specific antirheumatic drug treatment (60 outpatients). Correlation data based on 7 clinical variables suggest that PV estimations are at least as reliable as ESR and CRP in terms of diagnosis and as indices of improvement. The methodological advantages offered by the PV test lend support to its application in RA.