Several anticitrullinated protein/peptide antibodies (ACPA) assays have been reported to be of diagnostic value for rheumatoid arthritis (RA). We evaluated the technical performance and diagnostic accuracy of 6 ELISAs for the detection of antibodies to citrullinated protein/peptide antigens.
ACPA were determined in 298 serum samples using 6 commercially available ACPA assays. One hundred two samples were from RA patients, including patients with early and established RA, and 196 were from controls, including patients with psoriatic arthritis, connective tissue diseases, organ-specific autoimmune diseases, and a group of consecutive patients for whom a rheumatologist ordered anticyclic citrullinated peptide (CCP) antibodies. The ELISA reagent sets under study were Citrullinated Protein Antibodies (Genesis), Anti-MCV (Orgentec), Immunoscan RA (Euro-Diagnostica), Anti-CCP IgG ELISA (Euroimmun), EliA CCP (Phadia), and Quanta Lite CCP3 IgG ELISA (Inova). Technical performance (imprecision, linearity, correlation, and agreement) and diagnostic accuracy (sensitivity and specificity) were compared.
Variable technical performance was noted among the different ACPA assays, with some assays displaying poor reproducibility and bad linearity. ACPA results were well correlated among assays with the same antigen specificity, but the numerical values reported for each assay differed widely. Using cutoff values proposed by the manufacturer, diagnostic sensitivities ranged between 69.6% and 77.5% and specificities between 87.8% and 96.4%. The areas under the ROC curves were comparable among the different assays.
Overall diagnostic performance of ACPA assays is comparable among the different assays, but standardization is needed. For some assays, analytical characteristics could be improved.