Significance of rheumatoid factors in an eight-year longitudinal study on arthritis.

A community-based cohort comprising 150 patients with recent-onset seropositive arthritis or seronegative oligoarthritis or polyarthritis was monitored for 8 years. Of the different rheumatoid factor (RF) tests, the initial positivity in the most sensitive assays (latex slide test and IgM-RF by enzyme immunoassay) was the most reliable factor when distinguishing between the erosive and nonerosive cases. The individual RF isotypes fluctuated in four serial specimens, but each patient tended to preserve his or her reactivity pattern. Seroconversion from positive to negative within the 1st year of follow-up did not indicate a particularly good long-term prognosis.