[Sero-epidemiological study of the variability of rheumatoid factors].

Serum rheumatoid factors (RF) are occasionally observed in normal individuals. The clinical significance of the appearance of RF in the general population was examined in relation to the pattern of their appearance and the age of the onset of RA. A screening for RA in the residents of Yoshimatsu-Cho, Kagoshima Prefecture (population, 4,798), showed a prevalence of 0.29%, but the sera of 128 (4.0%; 3.4% for males and 4.5% for females) of 3,200 residents obtained at the screening were positive for RF, and the percent positivity tended to increase with age. The age of the onset of RA in 466 patients exhibited a nearly normal distribution with a peak in the 40's. From these findings, RF-positive individuals in the general population may be divided into a small group predisposed to RA and a great majority in whom the positivity is simply an age associated physiologic change.