Anti-cyclic citrullinated peptide antibodies: a comparison of different assays for the diagnosis of rheumatoid arthritis.

ABSTRACT

OBJECTIVES: Anti-cyclic citrullinated peptide (anti-CCP) antibodies are highly specific markers of rheumatoid arthritis (RA). Considering the heterogeneity of the target antigens involved, and the test platforms and conjugates proposed in commercial anti-CCP assays, we assessed the diagnostic performances of four fully automated anti-CCP assays in a cohort of patients with RA compared to patients with other autoimmune and inflammatory disorders. We also evaluated the agreement between the qualitative results of these immunoassays. METHOD: We evaluated three anti-CCP2 assays [Eurodiagnostica enzyme-linked immunosorbent assay (ELISA), Elecsys electrochemiluminescence immunoassay (ECLIA) on the Modular E170 Analyzer, and Zenit chemiluminescence immunoassay (CLIA) on the Zenit RA Analyzer] and one anti-CCP3 assay (Inova ELISA). ELISAs were performed on an automated workstation. Samples from 112 patients with RA and a disease control group of 136 patients (53 with autoimmune diseases, 65 non-autoimmune disorders, and 18 infectious diseases) were studied (included 161 samples submitted consecutively to the laboratory). RESULTS: At a fixed specificity of 92%, the anti-CCP3 assay presented the highest sensitivity (75%) compared to the anti-CCP2 assays evaluated (63-72%). The Zenit anti-CCP2 assay gave the most false-positive results (especially in patients with viral infections and connective tissue diseases). The agreement between assays ranged from 86.3% to 95.2% and Kappa coefficients ranged from 0.724 to 0.899. CONCLUSIONS: Recently released automated workstations provide a valuable alternative to ELISA to diagnose RA. However, differences in diagnostic performances are highlighted in our experience, especially for the Zenit assay. In our cohort, the anti-CCP3 assay gave slightly better performances than the anti-CCP2 assays (with the exception of the Zenit assay).