Anti-CCP: A Specific Marker of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease in which inflammation of the joint synovium can lead to joint damage. Late diagnosis and delayed treatment increase the risk of permanent loss of function. Persistent joint swelling warrants timely rheumatology assessment.

Laboratory tests support diagnosis, but no single test independently confirms or excludes RA. Rheumatoid factor (RF), measured by latex agglutination, turbidimetry or immunoassay, may also occur in other autoimmune diseases, chronic infections and some healthy people, particularly older adults. Conversely, some patients with RA have no detectable RF. A negative RF result does not mean the disease is absent.

Citrullination and Autoantibodies

Citrullination is the post-translational conversion of arginine residues into citrulline by peptidylarginine deiminase enzymes. It can affect fibrinogen, collagen peptides, filaggrin, vimentin and other proteins. Citrullination itself is not exclusively pathological or specific to RA.

In some patients, the immune system produces antibodies to citrullinated proteins (ACPA). Synthetic cyclic citrullinated peptides (CCP) are among the antigens used to detect them. The anti-CCP test identifies these autoantibodies and helps distinguish RA from other causes of joint symptoms.

Understanding the Result

Anti-CCP is generally more specific for RA than RF, but sensitivity and specificity depend on the assay, cutoff and population tested. Universal figures of at least 95.5% and at least 91.5% cannot be applied to every method. A positive result supports diagnosis in the appropriate clinical setting, but may also occur without established RA. A negative result does not exclude seronegative RA.

Antibodies may appear before clinical symptoms; this does not mean everyone testing positive will develop the disease. Diagnosis is based on examination, the pattern and duration of synovitis, inflammatory markers (ESR and CRP), RF/anti-CCP and imaging. Testing should not delay specialist referral when persistent inflammatory arthritis is suspected.