Background: Anticyclic citrullinated peptide (anti-CCP) is a relatively new serologic marker, which has been proposed for use in the diagnosis of rheumatoid arthritis (RA) and is said to be a highly specific.
Objective: The aim of the study was to evaluate the role of anti-CCP in a South Indian population of patients with suspected RA in the early stages when rheumatoid factor is negative and clinical presentation is atypical.
Methods: Patients with early inflammatory arthritis who were rheumatoid factor-negative were investigated for anti-CCP. The patients were reviewed by a rheumatologist and, based on American College of Rheumatology criteria, were diagnosed with RA or another disease after a follow-up period of 3 to 6 months. The rheumatologist was blinded to the results of the anti-CCP. The sensitivity and specificity of anti-CCP was estimated in comparison to follow up and final clinical diagnosis. The anti-CCP was estimated by the enzyme-linked immunosorbent assay method using a commercially available kit (Euroimmune).
Results: One hundred forty-three patients with a mean age of 47.1 years and a male to female ratio of 0.22:1 were recruited for the study. Thirty cases were positive for anti-CCP and 41 cases were finally diagnosed RA. Twenty-six of the 30 anti-CCP-positive patients were diagnosed with RA. Thus, the sensitivity of anti-CCP in our institution for the diagnosis of RA in the early stage in a group of rheumatoid factor-negative patients with atypical presentation was 63.4% with 36.6% false-negatives and the specificity was 96.1% with 3.9% false-positive cases. The positive predictive value of anti-CCP was 86.7% and the negative predictive value was 86.7%. Kappa statistic of agreement, chi McNemar test, indicated anti-CCP to be an efficient test in this study population.
Conclusion: Anti-CCP is a useful and highly specific but not absolutely specific or sensitive test to detect RA and supplements rheumatoid factor in the presence of a strong clinical suspicion.