Anti‐CCP2 is an adjunct to, not a surrogate for, rheumatoid factor in the diagnosis of rheumatoid arthritis: diagnostic utility of anti‐CCP2 antibodies in Egyptian patients with rheumatoid arthritis

Abstract

Objectives: 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.

Methods: 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.

Results: 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 (κ = 0.42, p<0.001) but agreement was only 66% for RA patients (κ = 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.

Conclusion: 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.