An indirect solid-phase microradioimmunoassay for human IgM-anti-IgG (rheumatoid factor).

In order to satisfy the general need for a more precise measurement of the serum concentration of rheumatoid factor (RF) than is presently obtainable with the latex test, we developed a rapid indirect solid phase micro radioimmunoassay for RF determination. The assay involves the binding of IgM-anti IgG (RF), to the polyclonal, native or denatured human IgG dried on the bottom surface of microtiter plates; the amount of antiglobulin bound is then determined by adding 125I-labelled goat anti-human IgM (125I-AHIgM). Variations of reagents and their concentrations, temperatures and incubation times were studied to find the optimal conditions for test sensitivity, specificity and reproducibility. The test has a within day and between day average coefficient of variation of 9 and 15% respectively, showing its advantages over the latex test. The results obtained by studying 100 human sera from patients with positive or negative latex test show that the test should prove valuable in diagnosis and research.