RESUMEN
BACKGROUND: The Rheumatoid Factor (RF) is the only serological marker in the diagnosis of rheumatoid arthritis (RA), but its sensitivity and specificity are not satisfactory for the diagnosis of RA. Therefore, we investigated the diagnostic performance of a new anti-cyclic citrullinated peptide antibodies test (anti-CCP) by the enzyme-linked immunosorbent assay (ELISA) in RA. METHODS: A cyclic peptide variant that contains citrulline was used as an antigenic substrate in ELISA. We performed the RF and anti-CCP in 324 RA patients, 251 non-RA patients (rheumatic diseases other than RA), and 286 normal individuals. Diagnostic performances such as sensitivity and specificity were evaluated by the receiver-operator characteristics (ROC) curve at optimal cut-off values. The optimal cut-off values were determined at the maximal point of the area under the curve. RESULTS: The sensitivity and specificity of anti-CCP were 72.8% and 92% at 3.8 U/mL. The sensitivity and specificity of RF were 80.6% and 78.5% at 9 U/mL. The sensitivity and specificity of anti-CCP and RF were 67%, 95.2% and 63.3%, 90% at 8.4 U/mL, 20 U/mL, respectively. A combination of anti-CCP with RF increased the sensitivity and specificity to 79.3%, 96.4%, respectively. Anti-CCP was positive in 23.8% among 63 sero-negative RA patients. CONCLUSIONS: We considered that the anti-CCP might be useful as another new serological marker for the diagnosis of a RA combination with RF, or not, because the anti-CCP has a higher diagnostic specificity than the RF and was an easy, convenient ELISA method in performance.