Clinical utility of the anti-CCP assay in patients with rheumatic diseases.

OBJECTIVES To determine the frequency of antibodies to cyclic citrullinated peptides (CCP) in a group of patients with a diversity of rheumatic diseases. METHODS 249 consecutive sera from an arthritis clinic sent for rheumatology testing were selected for testing with the anti-CCP2 assays and for the presence of rheumatoid factor (RF). Patient charts were reviewed for demographic information, clinical diagnosis, radiographic information, and other laboratory data. RESULTS The sensitivity and specificity of anti-CCP reactivity for the diagnosis of rheumatoid arthritis (RA) were 66.0% and 90.4%, respectively. This compared with the sensitivity and specificity of RF for RA at 71.6% and 80.3%. Furthermore, 10/29 (34%) RF- patients with RA demonstrated reactivity to CCP. The presence of either anti-CCP or RF increased testing sensitivity for diagnosis of RA to 81.4%; the presence of both RF and anti-CCP demonstrated a testing specificity similar to that of anti-CCP reactivity alone for the diagnosis of RA (91.1%). CONCLUSIONS The detection of anti-CCP is useful for the diagnosis of RA, in fact even more so than RF, because of its higher specificity.