Synovial fluid levels of anti–cyclic citrullinated peptide antibodies and IgA rheumatoid factor in rheumatoid arthritis, psoriatic arthritis, and osteoarthritis

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Abstract
Objective To assess the levels of anti–cyclic citrullinated peptide (anti-CCP) and IgA rheumatoid factor (IgA-RF) in synovial fluids of patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA), and osteoarthritis (OA). Methods Knee effusions of 29 patients with RA (23 women, 6 men; mean ± SD age 60 ± 15 years), 20 with PsA (6 women, 14 men; mean age 51 ± 12 years), and 19 with OA (9 women, 10 men; mean age 73 ± 11.8 years) were aspirated, tested for white blood cell (WBC) counts, centrifuged, and stored at −20°. Sera of 22, 11, and 12 of these patients with RA, PsA, and OA, respectively, were similarly stored. IgG anti-CCP and IgA-RF were detected by enzyme-linked immunosorbent assay. Erythrocyte sedimentation rate and C-reactive protein levels were used as measures of disease activity. Results Mean levels of synovial fluid anti-CCP and IgA-RF were significantly increased in RA joint effusions compared with PsA and OA (anti-CCP: 150 ± 134, 34 ± 29, and 24 ± 26 units, respectively [P < 0.003]; IgA-RF: 76 ± 77, 15.7 ± 10, and 18 ± 20 units, respectively). No significant difference was noted between OA and PsA. A significant correlation was found between synovial fluid anti-CCP and serum anti-CCP and IgA-RF. In patients with RA, a significant correlation was found between synovial fluid WBC counts and IgA-RF (P = 0.03) and serum IgA-RF (P = 0.008), but not between synovial fluid and serum anti-CCP levels. In RA patients, C-reactive protein correlated with serum IgA-RF. Conclusion Anti-CCP and IgA-RF were significantly increased in synovial fluid of RA in comparison with PsA and OA patients.

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