Measure of rheumatoid factor in human sera by passive haemagglutination of human erythrocytes carrying immunoglobulin linked by chromic chloride.

Serum rheumatoid factor in sero-positive patients with rheumatoid arthritis may be measured by passive haemagglutination of trypsin-treated human red cells linked with heat-aggregated human IgG by chromic chloride. The results show excellent correlation with those obtained with the classical Rose-Waaler test. The sera may be tested unheated and do not require preliminary absorption with red cells. By this test procedure it should also be possible to analyse the species, allotypic and conformational specificity of different rheumatoid factors.