IgM, IgA and IgG rheumatoid factors in patients with rheumatoid arthritis and normal donors.

IgM, IgA, and IgG Rheumatoid Factors (RF) were measured by ELISA assay in serum from 26 patients with definite rheumatoid arthritis (RA) and 11 normal controls. IgM-RF was assayed by ELISA, radioimmunoassay, and also by the standard latex fixation test in all sera from RA patients. In patients with RA quantitative amounts of IgM, IgA, and IgG-RF as estimated by ELISA were highly correlated. Significant correlations were found between a physician's rating of disease activity and IgG-RF (r = 0.44; p less than .02) and IgA-RF (r = 0.38; p = .06 but not for IgM-RF as measured in any of the three assays.