AntiCCP

Anti-CCP, or anti-cyclic citrullinated peptide antibodies, are autoantibodies directed against citrullinated proteins and peptides. Citrullination is a post-translational modification of arginine residues catalyzed by peptidylarginine deiminase enzymes and is associated with inflammatory processes in certain autoimmune diseases. Anti-CCP antibodies are most strongly associated with rheumatoid arthritis (RA) and are widely used as a serologic marker in its diagnosis and prognosis. The broader term ACPAs (anti-citrullinated protein antibodies) describes antibodies against citrullinated targets, with anti-CCP representing a common assay used to detect them.

Clinical use of anti-CCP testing centers on diagnosing RA in the appropriate clinical context and guiding prognosis. The test is typically used alongside clinical evaluation and other laboratory tests, such as rheumatoid factor (RF). Anti-CCP positivity supports the diagnosis of RA when symptoms are compatible, and its presence can precede symptom onset by years. In many laboratories, the CCP2 ELISA is the standard assay, though newer automated assays and other CCP variants are also employed.

Diagnostic performance is characterized by high specificity and variable sensitivity. Sensitivity for RA is commonly around 60–80%, depending on the assay and patient cohort, while specificity is typically about 95% or higher. High anti-CCP titers and persistent positivity are associated with a higher risk of radiographic progression and more erosive disease. Anti-CCP positivity is more common in seropositive RA; a substantial minority of RA patients are anti-CCP negative, and RF can be present without anti-CCP.

Limitations and considerations include possible false positives in some other autoimmune diseases and infections, and false negatives in early or seronegative disease. Serology should be interpreted with clinical findings, not used in isolation.