Background Rheumatoid factor (RF) is an autoantibody directed against the Fc component of IgG. It is present in approximately 70-80% of rheumatoid arthritis (RA) patients but also found nonspecifically in chronic inflammatory condition such as sarcoidosis, hepatitis B or C, and tuberculosis. Meanwhile, in relation to RA-related autoantibodies, airways abnormalities were reported in patients without inflammatory arthritis and the lung has been suggested as a potential site of generation of RA-related autoimmunity. In subjects without any specific medical problem, however, the influence of RF to lung function is infrequently known.
Objectives This study aimed to determine the effect of the presence of RF on pulmonary function in a large number of Korean healthy subjects without any history of joint disease and clinically apparent lung diseases.
Methods Of the 114,944 people who participated in a health checkup program in 2010, 94,438 subjects with normal chest radiography were recruited, whose results of RF and pulmonary function test (PFT) using spirometry were available. Subjects with arthralgia or the past medical history of arthritis including RA, and lung diseases were excluded based on self-reported questionnaire. Association between RF and PFT was assessed by correlation analysis.
Results Among 94,438 people, RF was positive in 3,326 subjects (3.52%). Their mean age was 41.3±8.3 (range, 21 – 83) and 43.8% were female; these characteristics were not significantly different from those of RF-negative subjects, whose mean age was 41.3±8.3 (range, 18 – 88) and 43.7% female. Ever-smokers (ex- and current smokers) were 39% in RF-positive subjects while 41.2% in RF-negative subjects (p=0.009). Hepatitis B surface antigen (HBsAg) and anti-hepatitis C antibodies (anti-HCV) were more frequently seen in RF-positive subjects (12.1% vs. 3.5%, p<0.001 for HBsAg and 0.5% vs. 0.1%, p<0.001 for anti-HCV). Regarding PFT, RF-positive subjects had lower forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) compared to RF-negative subjects (3.79±0.83 L vs. 3.87±0.83 L, p<0.001 and 3.17±0.66 vs. 3.25±0.67 L, p<0.001). The proportion of subjects with FVC below 82% and FEV1 below 84% of the predicted value was significantly higher in RF-positive subjects (50.7% vs. 46.6%, p<0.001 and 54.5% vs.49.4%, p<0.001) but the frequency of airflow limitation (FEV1/FVC ≤70%) did not differ between two groups (1.4% vs. 1.5%, p=0.47). FVC and FEV1 had negative correlations with the RF titers and the strength was very weak (r = -0.053, p<0.001 in FVC and r = -0.055, p<0.001 in FEV1).
Conclusions The results suggest that RF could impact on lung function in healthy subjects without clinically apparent lung diseases. A follow up study for the serial changes of PFT may reflect the actual influence of the raised RF titers.
Disclosure of Interest None declared