An ELISA for IgA-IgG and IgM-RF measurement. II. RF in several disease and control groups and under gold therapy in RA.

The before introduced solid phase ELISA was employed for the RF determination in the sera of RA patients and controls. The threshold values for positive results (calculated as the 95% distribution percentile of healthy donors) were 8, 3, and 3 U/ml for IgA, IgG, and IgM-RF, respectively. The results confirm the validity of the assay with clear negative results in several negative control groups (healthy donors, patients of the oto-, rhino-, laryngeal ambulance, diabetes mellitus, degenerative arthropathies; n = 111, median IgA, IgG and IgM-RF values of less than or equal to 2, less than or equal to 2 and less than or equal to 1 U/ml, respectively; 25-75% distribution percentiles within the median value) and positive results in the positive control group (seropositive RA; n = 20, median IgA, IgG and IgM-RF values of 324, 479 and 170 U/ml, respectively). 16/24 patients with so-called seronegative RA (negative Latex Fixation Test or Waaler Rose Test) had positive results in the ELISA, two of them had rheumatoid nodules clinically. The IgG-RF activity in the ELISA appears to be a good parameter for the course control of RA under gold therapy. 10 RA patients with clinical improvement of disease (declining ESR, CRP, joint index) after six months of gold therapy (= 0.6 g total gold amount) had a decline of total RF activity of 70% in median, whereas 10 patients with no clear effect on disease activity had only a decline of 20% in median.