The aims of our study were to compare in a cohort of 705 patients the diagnostic performance of two tests to detect autoantibodies to cyclic citrullinated peptides (CCP) and to determine whether a bead-based assay within a multiplex flow immunoassay (MFA) can be used instead of an enzyme linked immunosorbent assay (ELISA) technique in routine practice.
Six hundred and thirty patients with rheumatic symptoms and 75 patients with systemic lupus erythematosus (SLE) were tested for anti-CCP autoantibodies using two techniques: ELISA (Inova) and MFA (BioPlex, Bio-Rad).
Using kappa coefficient, there was an excellent agreement between ELISA and MFA when comparing 630 patients with rheumatic symptoms (κ coefficient, 0.82). In this cohort 174 patients were identified as suffering from RA, while 456 patients suffered from other diseases. Sensitivity and specificity values of anti-CCP autoantibodies for RA were 70.7% and 92.3% for ELISA and 64.4% and 92.8% for MFA. The positive and negative predictive values were 77.4% and 89.2% for ELISA and 77.2% and 87.2% for MFA, respectively. There were no differences in the diagnostic performances between the two assays (Z=0.67). The specificity values of anti-CCP autoantibodies analysing patients with SLE were 97.3% with MFA and 96% with ELISA with an excellent agreement between the methods (98.7%; κ coefficient, 0.79).
Concordance between ELISA and MFA is high in routine practice. Overall, MFA is a powerful tool for rapid assessment of anti-CCP autoantibodies and can replace the ELISA technique, which could be used as a second-line test in some cases.