Diagnostic value of synovial fluid anti-cyclic citrullinated peptide antibody for rheumatoid arthritis

Early and accurate diagnosis and treatment of rheumatoid arthritis (RA) improves disease outcome. Anti-cyclic citrullinated peptide antibody (anti-CCP) which is highly specific for RA is produced locally from inflamed synovium. The present study was designed to assess the diagnostic performance of synovial fluid anti-CCP (sf-CCP) for RA. A total of 128 patients consisted of 37 RA confirmed by the American College of Rheumatology revised criteria, 91 non-RA (50 non-RA inflammatory arthritis and 41 osteoarthritis) entered the study. Serum anti-CCP (sm-CCP) and Sf-CCP were measured by the ELISA method. Receiver operating characteristics curves were constructed to determine the optimal cutoff point levels for sf-CCP and sm-CCP to discriminate RA from non-RA. Diagnostic characteristics of both variables were determined by comparison of RA patients with non-RA controls. Mean levels of sf-CCP and sm-CCP were significantly higher in RA than in non-RA (P < 0.001). Sf-CCP discriminated RA from non-RA at the optimal cutoff value of 10 U/mL with high accuracy at AUC value of 0.897 ± 0.039, P < 0.001) sensitivity of 83.7% and specificity of 95.6%. Sm-CCP diagnosed RA at optimal cutoff level of 14.6 U/mL with respective sensitivity, specificity and AUC values of 84.8, 94.3% and 0.895 ± 0.049, P < 0.001). Sm-CCP was strongly correlated with sf-CCP (r = 0.75, r ² = 0.57, P < 0.0001). Two of 5 sm-CCP negative RA and 25.7% of serum rheumatoid factors negative RA were sf-CCP positive. These findings indicate that sf-CCP yields diagnostic ability as comparable as sm-CCP for RA. Respecting to local production of sf-CCP prior to disease onset, therefore sf-CCP determination may offer earlier as well as additional diagnostic information which may be more helpful in recognizing RA particularly among recent onset arthritis.