To examine the diagnostic utility of the second generation of anti-cyclic citrullinated peptide (anti-CCP2) antibodies versus rheumatoid factor (RF) in rheumatoid arthritis (RA), and to study the association between anti-CCP2 and RA disease parameters.
Fifty consecutive Egyptian patients with RA, 37 patients with other rheumatic diseases, and 10 healthy controls were recruited for testing for anti-CCP2 and immunoglobulin M (IgM) rheumatoid factor (RF). Assessment measures included the Disease Activity Score (DAS28) for disease activity, the Health Assessment Questionnaire - Disability Index (HAQ-DI) for disability and the Short Erosion Narrowing Score (SENS) for radiological damage.
The sensitivities of anti-CCP2 and IgM-RF in RA patients were 70% and 52%, with specificities of 91.5% and 89.4%, respectively. There was 73.2% agreement between anti-CCP2 and RF for all groups tested (kappa = 0.42, p<0.001) but agreement was only 66% for RA patients (kappa = 0.31, p<0.05). Anti-CCP2 had superior diagnostic properties [sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV)] than RF, but using both RF and anti-CCP2 enhanced the sensitivity to 78%, when either test was positive, and the specificity to 100%, with a PPV of 1, when both tests were positive. Anti-CCP2 titre was significantly correlated with disease severity [rheumatoid nodules, rheumatoid factor (RF), and radiological damage] and HAQ-DI (p<0.05) but not with parameters of disease activity.
Anti-CCP2 has superior diagnostic and prognostic properties in RA compared with RF. It should not replace RF as a serological test; however, since using both tests modestly increases sensitivity and markedly enhances specificity, so that diagnosis of RA is highly probable when both tests are positive.