Isotype-specific measurement of rheumatoid factor with reference to clinical features of rheumatoid arthritis.

Serum levels of IgG, IgA and IgM rheumatoid factor (IgG RF, IgA RF and IgM RF) were estimated by means of the diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA), in 90 Waaler-Rose positive and Waaler-Rose negative rheumatoid arthritis (RA) patients as well as in 60 controls. The presence of IgG and/or IgA RF was shown to be of high predictive value concerning the occurrence of systemic manifestations in RA. All RF isotypes measured were good indicators of the disease activity.