Are anti-citrulline autoantibodies better serum markers for rheumatoid arthritis than rheumatoid factor in Thai population?

The aim of the study is to evaluate the prevalence of anti-citrulline antibodies (anti-CCP) versus rheumatoid factor (RF) in a cohort of Thai patients with rheumatoid arthritis (RA), a variety of rheumatic diseases other than RA and healthy controls. The association between anti-CCP and RA disease activity was also examined. Serum from 125 RA patients, 60 from other rheumatic diseases (non-RA) and 60 from healthy controls were tested for IgM RF and second generation anti-CCP. The association between anti-CCP, RF, the Disease Activity Score (DAS 28) and other relevant laboratory tests (CBC, ESR and CRP) were assessed. The sensitivity and specificity of anti-CCP antibody were 58.7 and 100% when compared with 63.5 and 98.3% for RF. These differences were not statistically significant. The anti-CCP outperformed RF in terms of the positive-predictive values (100 vs. 97.6%); however, the negative-predictive values were 72.4% for RF and 69.6% for anti-CCP. The sensitivity when either anti-CCP or RF was positive increased to 71.2%. Nine out of 45 RF-negative patients had a positive anti-CCP test. Anti-CCP was significantly correlated with parameters of inflammation, but not with DAS 28. In conclusion, although anti-CCP is better than RF in distinguishing RA from other rheumatic diseases, its cost, which is 3.3 times higher than the RF test precludes it from replacing RF as a serum marker for Thai patients with RA. The treatment decisions cannot be based on the test alone, as it has no correlation with DAS 28. Its usefulness is in patients with suspected RA who have had a negative RF test.