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°C and then incubated with ¹²⁵I-labelled heat-aggregated 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 < 0.01) was observed between the rheumaton titre and the RF-RIA result.