Prevalence and clinical significance of anti-SSA antibody in the Chinese health screening population

Anti-Sjögren's syndrome type A (anti-SSA) antibodies are non-organ-specific autoantibodies highly prevalent in various autoimmune diseases. This study primarily investigated the prevalence of anti-SSA antibodies in the health screening population. Additionally, we explored the clinical features of the anti-SSA antibody-positive population and evaluated the development of connective tissue diseases (CTD) over the years in individuals with anti-SSA antibodies for whom follow-up was available. A total of, 64 045 individuals without a history of CTD from 2013 to 2022 who visited Peking Union Medical College Hospital for health screening were screened for autoimmune antibodies: 1.7% (1091/64 045) of the Chinese health screening population were positive for anti-SSA antibodies, with a prevalence of 0.9% (290/33 829) in men and 2.7% (801/30 216) in women. Compared with matched autoantibody-negative controls, anti-SSA antibody-positive individuals had higher levels of serological abnormalities, including erythrocyte sedimentation rate (ESR) [10 (6-15) mm/h vs. 7 (4-12) mm/h, P < 0.0001], rheumatoid factor (RF) [7.15 (4.30-16.90) IU/ml vs. 5.00 (3.20-7.90) IU/ml, P < 0.0001], and immunoglobulin G [13.09 (11.20-15.45) g/L vs. 11.34 (9.85-13.18) g/L, P < 0.0001], and lower levels of white blood cells (WBC; 5.49 ± 1.50 × 109/L vs. 5.82 ± 1.49 × 109/L, P < 0.0001). Additionally, they had a higher proportion of coexisting thyroid autoantibodies, including anti-thyroid peroxidase antibodies (TPO-Ab) (17.1% vs. 11.3%, P < 0.0001) and anti-thyroglobulin antibodies (Tg-Ab) (17.8% vs. 11.0%, P < 0.0001). Among the 381 subjects who were anti-SSA positive and followed up for a median of 4.6 years, 146 (38.3%) individuals developed CTD, including 68 (17.8%) cases of primary Sjögren's syndrome (pSS), 10 (2.6%) cases of rheumatoid arthritis (RA), 5 (1.3%) cases of systemic lupus erythematosus (SLE), 4 (1.0%) cases of secondary Sjögren's syndrome (sSS), and 59 (15.5%) cases of undifferentiated connective tissue disease (UCTD). In all, 235 (61.7%) individuals did not develop CTD over a median time of 5.9 (2.9-8.1) years after the earliest autoantibody detection. Elevated ESR (>20 mm/h), RF positivity (>20 IU/ml), and female gender were identified as independent risk factors for CTD among the anti-SSA antibody-positive individuals. Anti-SSA antibodies were found in 17 among approximately 1000 individuals without a history of autoimmune diseases. Anti-SSA antibody-positive individuals are advised to periodically monitor thyroid function. Elevated ESR (>20 mm/h), female gender, and RF positivity may delineate a high-risk cohort for CTDs.