A simple radioactive binding assay for the detection of rheumatoid factor in serum

A simple radioactive binding assay for the detection of rheumatoid factor (RF-RBA) is described. Test sera are complement inactivated by incubation in 0.13 M ethylene diaminetetraacetic acid (EDTA) at 37 degrees C and then incubated with 125I-labelled heat-aggregated IgG. Rheumatoid factor bound, labelled IgG is separated from free by precipitation with 2.5% (w/v) polyethylene glycol 6000. Sera from 78 patients and 24 controls were tested in the RF-RBA assay and the results compared with those obtained by the rheumatoid latex test and the rheumaton test. 37 sera were positive and 59 sera were negative for rheumatoid factor by the 3 methods used. A positive correlation (r = 0.56, P less than 0.01) was observed between the rheumaton titre and the RF-RIA result.