[Clinical significance of IgG rheumatoid factor in patients with rheumatoid arthritis]

We studied 135 patients with rheumatoid arthritis (RA) from February 1991 through June 1992 (mean period: 9 months) to measure serum IgG rheumatoid factor (IgG-RF) by the method of enzyme linked immunosorbent assay. In order to evaluate clinical significance of serum IgG-RF we compared the level of IgG-RF with some of the clinical and laboratory markers including disease activity index of RA and titers of IgM rheumatoid factor (IgM-RF) and IgA rheumatoid factor (IgA-RF). Positive IgG-RF (more than 2.0 on IgG-RF index) was observed only in 22.2% (30 patients) with the examination of the first collected serum samples but was increased to 41.5% (56 patients) by the case of total test samples. The number of patients with positive IgM-RF or positive IgA-RF test was significantly smaller in seronegative patient group than in seropositive patient group, whereas IgG-RF test showed no significant differences between these two groups. These indicate usefulness of consecutive test of IgG-RF for diagnosis of RA especially in seronegative patients. The mean of total score indicating radiographic bone destruction by Sharp's modified method was significantly higher in positive patients than in negative patients of IgG-RF. Multivariate analysis showed positive correlations between serum IgG-RF levels and erythrocyte sedimentation rates as well as between serum IgG-RF levels and Lansbury's indexes. These results suggest that the test of serum IgG-RF level is beneficial for daily management of patients with RA.