To evaluate the diagnostic sensitivity of antibodies to cyclic citrullinated peptide (CCP) in recent onset rheumatoid arthritis (RA) at diagnosis and 3 years later, and to evaluate anti-CCP antibody as a predictor of the disease course during 3 years.
242 patients with recent onset (< or =1 year) RA were followed up regularly during 3 years after inclusion in the Swedish multicentre study "TIRA" 1996-98. Anti-CCP antibodies were analysed by an enzyme immunoassay (EIA). Rheumatoid factors (RFs) were analysed by latex agglutination and two isotype-specific (IgM and IgA) EIAs. Disease activity was assessed by plasma CRP, ESR, 28 joint disease activity score, and the physician's global assessment of disease activity. Functional ability was evaluated by the Health Assessment Questionnaire.
Overall, the diagnostic sensitivity of anti-CCP antibodies was 64% and the proportion of positive tests increased with the number of fulfilled classification criteria according to the American College of Rheumatology. The anti-CCP antibody results correlated with RF, but were better than RF as predictor of a more aggressive disease course. After 3 years 5/97 patients had changed anti-CCP status: 2 from negative to positive and 3 from positive to negative. The mean level of anti-CCP antibodies declined by 131 U/ml during the 3 year follow up (95% CI 34 to 228 U/ml).
The anti-CCP antibody assay has a similar diagnostic sensitivity to that of RF in early RA, but is better as a predictor of the disease course over 3 years. Although the mean serum level declines, anti-CCP antibody positivity remains essentially unaltered 3 years after diagnosis and start of antirheumatic treatment.