Prevalence of rheumatoid factor and parameters associated with rheumatoid factor positivity in Korean health screening subjects and subjects with hepatitis B surface antigen

Objectives The purpose of this study is to assess the prevalence and titer of rheumatoid factor (RF) in Korean health screening subjects and consecutive subjects with hepatitis B surface antigen (HBsAg) and to examine the factors influencing RF positivity. Methods This study was performed in 37,660 patients (23,269 men, 14,391 women) without arthralgia, who participated in a health checkup program in 2009. Results Approximately 3.7% of health screening subjects (3.3% of males and 4.4% of females) were positive for RF. Among subjects with HBsAg (n = 1,494) and antibody for hepatitis C virus (HCV) (n = 132), 11.8 and 10.6% were RF positive, respectively. There was a significant difference in the RF-positive rate between males and females. The RF-positive rate had a significant linear-by-linear association with aging, but there was no significant relationship between RF positivity and aging among subjects with HBsAg or anti-HCV antibody. Presence of HBsAg and anti-HCV antibody, positive C-reactive protein (CRP), and female sex were factors strongly associated with RF positivity. Conclusions The rate of RF positivity in health screening adults and subjects with HBsAg in Korea can be estimated to be 3.7 and 11.8%, respectively. Clinicians should consider hepatitis B or C virus infection status, CRP positivity, and sex when interpreting RF-positive results.