[Incidence of serum rheumatoid factors in elder non-rheumatic individuals].

With the aging of the Japanese population, an increase in the number of elderly patients with rheumatoid arthritis (RA) has been noted in recent years. Although rheumatoid factor (RF) is found in a high proportion of RA patients, it is also known to be present in non-rheumatoid patients. However, no studies have investigated the rate of RF positivity in elderly non-rheumatoid individuals. In this study, we examined the rate of RF positivity in such individuals and the association between smoking and RF production. The subjects were 25 men (aged 67 to 87 years, with a mean of 74.0) and 24 women (aged 60 to 86 years, with a mean of 70.7). Of these subjects, nine (18.4%), including seven men, were RF-positive. A significant positive correlation was observed between age and RF values (n=49, p<0.05). Of 23 subjects with a smoking habit, eight (34.8%) were RF-positive. In contrast, only one (3.8%) of 26 nonsmokers was RF-positive. This difference in the rate of RF positivity was significant (p<0.01). In addition, a significant positive correlation was noted between the duration of smoking and rate of RF positivity (p<0.05), particularly in men (p<0.01). These results suggest that smoking is closely involved in RF production in the elderly.