IgM, IgG and IgA rheumatoid factors (antiglobulins) in early rheumatoid arthritis and their production of articular index over one year.

An enzyme-linked immunosorbent assay was used to detect antiglobulins (rheumatoid factors, RF) of various classes in 33 patients with recently diagnosed rheumatoid arthritis and to follow their progress with 3-monthly checks for 1 year. For RF, IgA-RF and IgM-RF showed greater sensitivity than the latex test, either or both being positive in 76%. There was no correlation between any of the measures of RF and patient's clinical status as judged by articular index (AI), or serum CRP level. For individual patients, RF levels varied considerably between assessments. The best predictors of clinical status over 1 year were the initial AI and the latex test for RF. While class-specific measurement of RF is more sensitive than the latex test, the variation of individual classes of antiglobulins over time within individual patients makes them less helpful as predictors of disease progress.