The Role of Synovial Fluid Levels of anti-cyclic Citrullinated Peptide Antibodies in Differential Diagnosis of Arthritis

Abstract

Objectives: To determine the usefulness of anti-cyclic citrullinated peptide antibodies (anti-CCP) in synovial fluid (sfCCP) for differential diagnosis of variable arthropathies, and to analyze the correlations with anti-CCP and rheumatoid factor (RF) in serum as well as white blood cells (WBC) counts in synovial fluid. Methods: 191 synovial fluid samples were tested for WBC counts and anti-CCP using anti-CCP2 assays. Sera of the 43 patients with rheumatoid arthritis (RA) were additionally tested for anti-CCP (smCCP) and RF. Results: The sfCCP levels were within the normal limit in patients with osteoarthritis, seronegative spondyloarthropathy, gout, Behcet's disease, systemic lupus erythematosus, CPPD disease, infection, osteonecrosis, pigmented villonodular synovitis and undifferentiated connective tissue disease, except one with gout (1/57, 2%). The sfCCP of RA patients were distinctively higher than those in other arthritis groups (p＜0.0001). The positive rate of sfCCP, smCCP and RF in serum in RA patients was 79% (34/43), 83.7% (36/43) and 72.1% (31/43), respectively. In RA patients, sfCCP was strongly correlated with smCCP (p＜0.001), RF moderately (p＜0.05), but not correlated with total WBC, polymorphonuclear cell or mononuclear cell counts in synovial fluid. Conclusion: sfCCP is highly specific for RA, and is closely related to smCCP and RF, but not correlated to the numbers of PMN, which are considered to offer peptidyl-arginine deiminase 4 and induce citrullinated protein formation in the murine model.