Rheumatoid factor activity by rate nephelometry correlated with clinical activity in rheumatoid arthritis

The purpose of this study was to evaluate, prospectively, the clinical usefulness of the rate nephelometric method for determining rheumatoid factor (RF) activity, measured in International Units (IU), in patients with rheumatoid arthritis. These results were compared with those of standard latex agglutination titration. The overall correlation between clinical activity and RF activity measured by rate nephelometry and serologic titration are similar, i.e., r = 0.47 (P less than 0.001) and r = 0.43 (p less than 0.001), respectively. However, on an individual patient basis, the nephelometric determination appears to correlate better with disease activity and response to therapy than do titers. The RF activity measured in IU would give the clinician a more sensitive and precise tool with which to follow RF activity in individual patients with active disease.