prevalence and diagnostic performance of anti-cyclic citrullinated peptide antibody in rheumatoid arthritis: the predictive and discriminative ability of serum antibody level in recognizing rheumatoid arthritis

ABSTRACT

The utility of anticyclic citrullinated peptide [anti-CCP] antibody in the diagnosis of rheumatoid arthritis [RA] varies across different studies. We determined the diagnostic performance and predictive ability of anti-CCP for RA. We studied 201 patients with RA and compared them with 208 non-RA patients as controls. RA patients included in the study fulfilled the American College of Rheumatology revised criteria and patients with other diseases as well as those with undifferentiated arthritis [UIA] were used as controls. Anti-CCP was measured by enzyme-linked immunosorbent assay [ELISA] and rheumatoid factor [RF] by the agglutination method. The optimal cutoff value and diagnostic accuracy were determined using receiver operating characteristics [ROC] curve and area under the curve [AUC].The sensitivity and specificity were determined by comparison of RA patients with non-RA controls. The anti-CCP test was positive in 164 patients with RA for a sensitivity of 81.6%, specificity of 87.5%, and overall accuracy of 84.6%. The respective values for RF were 75.6%, 86.5% and 84.4%. The anti-CCP test discriminated RA from non-RA patients with high accuracy [AUC=0.889 [0.017] 95% CI, 0.856-0.952, P=.001], and predicted progression of UIA to RA with moderate accuracy [AUC=0.733 [0.069], 95% CI 0.60-0.87, P<.006] at a sensitivity of 75% and a specificity of 68.1%. Among 60 UIA patients, in 16 [26.7%] who differentiated to RA, the mean [standard deviation] for anti-CCP was significantly higher than in 24 [40%] patients who progressed to non-RA [134.8 [172] vs 46 [86] U/mL, P<.01]. These findings indicate that anti-CCP yields higher sensitivity and overall accuracy, but slightly greater specificity than RF for diagnosis of RA. Anti-CCP positivity, particularly a higher level of serum antibody in patients with UIA, may be a predictor of subsequent RA