Objective: The assay for anti-cyclic citrullinated peptide (anti-CCP) antibody is a recent test of interest due to low diagnostic specificity of rheumatoid factor in the diagnosis of rheumatoid arthritis. To determine the sensitivity and specificity of anti-CCP antibodies in rheumatoid arthritis patients using American College of Rheumatology (ACR) criteria as a gold standard.
Design: A cross sectional study was conducted from January 2008 to December 2008 on 100 patients with rheumatoid arthritis and 153 patients with arthritis or arthralgia but not fulfilling ACR criteria for rheumatoid arthritis.
Materials and Methods: Serum from each subject was tested for anti-CCP antibodies and IgM rheumatoid factor (IgM RF) by an enzyme linked immunosorbent assay (ELISA). Sensitivity and specificity of the tests were evaluated using the ACR criteria as the gold standard. Data was analyzed using SPSS version 12.0 software. The association between the two categorical variables were tested using chi-square test. The differences between the two groups were tested using independent t-test. Results: The sensitivity of anti-CCP antibodies was 71% with 94.8% of specificity. For rheumatoid factor the sensitivity was 85% and the specificity was 74.5%. Positive predictive value for anti-CCP antibodies was 89.9% whereas for rheumatoid factor it was 68.5%. The sensitivity of ACR criteria with inclusion of anti- CCP antibodies was 100% and specificity of 94.8% (95%CI: 91.3%, 98.2%).
Conclusion: Anti-CCP antibody has a higher diagnostic accuracy compared to the RF. Anti-CCP antibody is a useful laboratory marker to support the diagnosis of rheumatoid arthritis and to differentiate patients with rheumatoid arthritis from rheumatoid arthritis-like symptoms. Therefore, it is suggested that anti-CCP antibodies should be included as another laboratory supportive criterium besides RF test in ACR criteria in the diagnosis of RA.
Study site: family medicine clinic, rheumatology clinic and immunology laboratory of Hospital Universiti Sains Malaysia (HUSM), Kubang Kerian, Kelantan, Malaysia