Anti-cyclic citrullinated peptide (CCP)2 antibody status is an important diagnostic tool in the work-up of undifferentiated arthritis (UA)/early rheumatoid arthritis (RA) but the results of the enzyme-linked immunosorbent assay (ELISA) are only available a few days after the test. The aim of this study was to assess the measurement characteristics of a rapid anti-CCP2 test compared to the usual anti-CCP2 ELISA test.
In the first phase, rapid anti-CCP2 (CCPoint) tests were performed in capillary blood obtained by finger puncture (CAP), in venous blood from a clot tube (CLOT) and in serum (SERUM) in consenting RA patients. Anti-CCP2 measured in serum using the anti-CCP2 ELISA (ELISA) was set as the gold standard (reference). In the second phase of the study, specificity versus RA was confirmed in consenting non-RA patients and healthy controls. The anti-CCP2 results were negative (no visible line or anti-CCP2<25 U/mL) or positive (visible line or anti-CCP2> or =25 U/mL).
A total of 880 subjects (109 RA patients, 351 non-RA patients and 420 healthy controls) were enrolled in this study. For the RA patients, 5%, 15%, and 1% of CAP, CLOT and SERUM tests, respectively, were inconclusive. The sensitivity and specificity of CAP compared with ELISA were 95% (95% CI 90-100) and 95% (95% CI 89-100), respectively, and the corresponding values for SERUM were 97% (95% CI 93-100) and 98 (95% CI 94-100). The specificity for RA versus non-RA and healthy controls was 99% (95% CI 97-100) and 99% (95% CI 98-100), respectively.
The CCPoint test is a fast, valid and reliable anti-CCP2 test in both capillary blood and serum but not directly in venous blood.