IgA rheumatoid factor as predictor of disease activity.

IgA rheumatoid factor (RF) was shown to occur in rheumatoid arthritis (RA) sera in 1963, but for almost 20 years thereafter this RF isotype received little attention. Solid-phase immunoassays, esp. ELISA, are now widely used for the detection of serum IgA RF which may be raised in RA, primary Sjögren's syndrome, systemic lupus erythematosus (SLE) and several other diseases. Over the past four years the following observations on IgA RF have been published: While IgM RF levels showed positive correlation with age, IgA RF levels did not. Gold therapy reduced IgA RF levels but the relationship to clinical improvement was not clear. In longitudinal studies, changes in overall disease activity, Ritchie articular index, grip strength and ESR showed a closer association with IgA RF than with IgM RF. Five groups have reported an association between IgA RF and the severity of erosive arthritis. In early RA, IgA RF may be a more specific predictor of disease severity than IgM RF or IgG RF. Further work is needed on the occurrence and biology of IgA RF, but measuring this isotype alone would improve the clinical specificity of routine RF tests.