Synovial fluid anti-citrulline-containing peptide antibody and its role in the diagnosis of rheumatoid arthritis

Objective This study aimed to measure the level of anti-citrulline-containing peptide (anti- CCP) antibody (ab) in the synovial fluid (SF) of rheumatoid arthritis (RA) patients to study its relations with anti-CCP ab serum level, RA disease activity, and severity parameters as well as to explore its diagnostic value in RA. Patients and methods This study was conducted on 60 RA and 60 osteoarthritis (OA) patients. Patients were subjected to thorough history taking and full clinical examination including locomotor system examination. The Health Assessment Questionnaire was used for the assessment of functional capacity. Complete laboratory investigations including a complete blood count, erythrocyte sedimentation rate, C-reactive protein, rheumatoid factor, serum and SF anti-CCP ab levels were carried out. The Sharp score was calculated for the assessment of RA severity in posteroanterior plain radiographic views of both hands and feet. Results The mean SF anti-CCP ab level was highly significantly increased (P=0.0001) in RA patients (133.93±41.3 ng/l) in comparison with OA patients (5±13.2 ng/l). There were statistically significant correlations of SF anti-CCP ab level with rheumatoid factor (P=0.049), serum anti-CCP ab (P=0.0001), and Sharp score (P=0.037), whereas other clinical and laboratory parameters did not show any significant correlation (P>0.05). The specificity of SF anti-CCP ab and serum anti-CCP ab of RA patients was 100%. Besides, the sensitivity of serum anti-CCP ab was 90%, whereas the sensitivity of SF anti-CCP ab was 83.3%. The positive predictive value of both serum and SF anti-CCP abs was 100% in RA patients and their negative predictive value was 90.9% in the serum of RA patients and 85.7% in the SF. The cutoff value of anti-CCP ab was 65.4 ng/l in the serum and 63.35 ng/l in the SF. Conclusion SF anti-CCP ab is significantly increased in RA compared with OA and could be considered an appreciated diagnostic marker having a major role in the identification of RA patients not fulfilling the criteria for the RA disease diagnosis. Its relation to RA disease severity could not be established.