An assessment of the diagnostic value of quantitative measurements of IgA rheumatoid factor.

IgA rheumatoid factor (RF) was found in a significant number of the normal population. As a consequence, the presence of IgA RF was not more specific for a diagnosis of rheumatoid arthritis than IgM RF. However, further investigation of IgA RF as a prognostic indicator is important. Our results, which show an association between the presence of IgA RF and higher levels of IgM RF, suggest that careful differentiation between the predictive values of the presence of IgA RF and a high level of IgM RF will be necessary.