Pertormanceof a New Rate-NephelometricAssayfor RheumatoidFactor, and ItsCorrelationwithTube-TiterResultsfor HumanSera and Synovial Fluid

We evaluated a rate-nephelometric assay for rheuma-toid factor (RF), as developed for use with the Beckman Immunochemistry System (ICS). Within- run precision (CV) for low-, mid-, and high-dilution samples (60-400 kilo-mt. units/L) was 3.5, 1.5, and 1.6%; between-run precision was 3.4%. Analytical linearity was excellent. Biological interference resulted in some degree of nonlinearity in more than 70 % of the patients ’ samples tested. Sensi-tivities were 96.5 and 94.1 % and specificities were 98.5 and 95.3 % for the ICS RF and Wampole slide methods, respectively, for a clinically defined population of 170 patients. Results for 100 ICS RF-positive samples corre-lated well with concomitantly measured Calbiochem-Behring tube-titers. Weekly measurement of Calbio-chem-Behring, Hyland Diagnostics, and ICL Scientifi