A comparison of performance of anti-cyclic citrullinated peptide 2 and citrullinated protein antibodies in the diagnosis of rheumatoid arthritis in Iranian patients

Antibodies to citrullinated proteins and rheumatoid factor (RF) are widely used in patients with rheumatoid arthritis (RA) and the antibodies to citrullinated proteins appear to be the most specific markers of the disease. The objective was to compare the diagnostic performance of the anti-cyclic citrullinated peptide 2 (anti-CCP2) and citrullinated protein Antibodies (CPA) with RF in the diagnosis of RA. Serum samples of 139 patients with RA and 131 patients with other rheumatic diseases were checked for anti-CCP2, CPA uses citrullinated recombinant rat filaggrin as the antigen assay, and RF. The specificity, sensitivity, and receiver operating characteristic (ROC) of tests were then compared. The sensitivity of anti-CCP2, CPA, and RF were 82.7, 83.5, and 61.5%, respectively. The specificities of the tests were 91.2, 78.6, and 90.5%, respectively. The area under ROC curves for the tests were 0.925, 0.890, and 0.847, respectively. Exclusion of overlaps was associated with improved specificity for CPA but no change in the specificity of RF and anti-CCP. The sensitivity of anti-CCP2, CPA, and RF were 66.7, 77.8, and 51.9% for patients with early RA, respectively. The findings of the present study indicate that anti-CCP2 might be of a better diagnostic value for the diagnosis of RA. They also showed that CPA and in the second place anti-CCP2 were useful in the diagnosis of early RA.