Laboratory diagnosis of rheumatoid arthritis: a solid phase radioassay for IgG and IgM antiglobulins.

A technique suitable for the routine estimation of IgM and IgG antiglobulins has been devised. The assay involves the binding of antiglobulins to plastic tubes coated with rabbit immunoglobulin: the amount of antiglobulin bound is then determined by adding radiolabelled antihuman IgG or IgM. The conditions for the assay have been examined and optimal incubation times and amounts of reagents established. Verification of the antibody nature of antiglobulin activity has been obtained. Both IgG and IgM antiglobulins were raised in virtually all seropositive rheumatoid arthritics, and most seronegative patients gave elevated values for either IgM or IgG rheumatoid factors. The use of an anti-light chain reagent as a screening test for total antiglobulins was investigated. These tests should prove valuable in diagnosis and permit quantitative evaluation of research studies.