Rheumatoid factor seroconversions in relation to clinical rheumatoid arthritis.

Two blood samples were taken with an interval of five years in a continuing epidemiological study of a rural population with an age range of 40-64 at the commencement. Paired sera from 1805 subjects were tested for rheumatoid factors using Waaler-Rose and latex tests. Simultaneous conversion in both tests from negative to positive occurred in seven cases and from positive to negative in eight cases, corresponding to 20% of the Waaler-Rose positives. The mean Waaler-Rose titre in the cases converting to positive was nearly four times higher than in the cases converting to negative. Five subjects developed Waaler-Rose-positive rheumatoid arthritis after the baseline survey. In three of them, positive rheumatoid factor reactions were observed to precede the joint disease; in two others the chronological order could not be established.