Predictive value of antibodies to cyclic citrullinated peptide in patients with early arthritis

The objective of this study was to determine the diagnostic value for rheumatoid arthritis (RA) of antibodies to cyclic citrullinated peptides (anti-CCP) in patients with early arthritis and vasculitis. Sixty-four adult patients with early arthritis and disease duration of less than 4 months were clinically diagnosed by an experienced rheumatologist as having RA (n=27), spondyloarthropathy (n=11), and undifferentiated arthritis (n=26). Eighteen patients with vasculitis were also included in the study. The patients with early arthritis were followed up for 9 months. After the follow-up period, five of 26 patients with undifferentiated arthritis were diagnosed as having RA. All serum samples were tested for anti-CCP and IgM rheumatoid factor (IgM-RF). The anti-CCP positivity in RA patients (44.4%) was significantly more frequent than in patients with undifferentiated arthritis (3.8%), spondyloarthropathy (0%), and vasculitis (5.6%) (p=0.001, p<0.01, and p<0.01, respectively). The frequency of IgM-RF positivity was 40.7% in RA, 7.7% in undifferentiated arthritis, 0% in spondyloarthropathy, and 22.2% in vasculitis groups. The respective specificity of anti-CCP and IgM-RF tests for early RA were 97.3 and 94.6%, and the respective sensitivity of them were 44.4 and 40.7%, respectively. The combination of anti-CCP and IgM-RF positivity had a very high specificity and positive predictive value (100%) but a rather low sensitivity (33.3%). When either anti-CCP or IgM-RF positivity combined into one criterion, the sensitivity became high (51.9%) but the specificity decreased to 91.9%. Overall performance of anti-CCP test alone for the early RA was higher than IgM-RF and the combination of anti-CCP and IgM-RF (p<0.05), and was similar to the combination of anti-CCP or IgM-RF. The specificity of positive anti-CCP test for diagnosis of established RA reached up to 100%. In conclusion, the anti-CCP test is a new diagnostic test with extremely high specificity for RA. Anti-CCP antibody testing combined with IgM-RF testing has additional value over IgM-RF testing alone in patients with early arthritis.