An improved assay for IgG rheumatoid factor: its value in the diagnosis of rheumatoid arthritis.

A simple radioimmunoassay suitable for the routine estimation of IgG rheumatoid factors (IgG RF) has been developed. This involves determination of the amount of IgG RF binding to highly purified human IgG Fc on microtiter plates using a radiolabelled F(ab')2 preparation of an antihuman IgG Fd antiserum. A correction for nonspecific binding is made by subtracting sample reactivity with bovine serum albumin. Significantly elevated IgG RF levels were found only in patients with symmetrical peripheral erosive polyarthritis and in some patients with "mixed connective tissue disease."