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.
OBJECTIVE
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 (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.


CONCLUSIONS
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.
Abdel-Nasser
A M
AM
Department of Rheumatology and Rehabilitation, Minia University, Egypt. ahmedabdelnasser@yahoo.com
Mahmoud
M H
MH
El Mansoury
T M
TM
Osman
A M
AM
D000293:Adolescent; D000328:Adult; D000368:Aged; D000888:Antibodies, Anti-Idiotypic / Q000097:blood* / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000175:diagnosis* / Q000276:immunology; D016022:Case-Control Studies; D004534:Egypt; D005260:Female; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000097:blood* / Q000276:immunology; D011379:Prognosis; D012217:Rheumatoid Factor / Q000097:blood*; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
D000888:Antibodies, Anti-Idiotypic; D007075:Immunoglobulin M; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D012217:Rheumatoid Factor