Objectives: We aimed to determine the prevalence of laboratory findings in a large group of patients with inflammatory arthritis (IA) and the sensitivity and specificity level of anti-cyclic citrullinated peptide (anti-CCP) antibodies and rheumatoid factor (RF) antibodies in the diagnosis of rheumatoid arthritis (RA).
Material and Methods: We recorded the medical findings of 4439 patients with IA, including their demographic and clinical characteristics as well as their laboratory test results. We assessed the inflammatory diseases of patients with positive anti-CCP antibodies tests.
Results: The medical records of 4439 subjects were analysed: the mean age was 49.06 ± 14.06 years, and the sensitivity and specificity of anti-CCP antibodies for the diagnosis of rheumatoid arthritis (RA) were 56% and 97%, respectively. This was compared with the sensitivity and specificity of RF for RA at 75% and 93%. The combination of anti-CCP antibodies and IgM RF resulted in a higher positive predictive value of 92% and a slightly lower negative predictive value of 93% as compared with the use of IgM RF alone. We detected spondyloarthritis in 27 (7.2%), Sjögren’s syndrome in 22 (6%), familial Mediterranean fever (FMF) in 13 (3.4%), and gout in 9 (2.4%) patients in the anti-CCP antibodies positive group.
Conclusions: Anti-CCP antibodies have a higher specificity than Ig RF for RA. Although rheumatoid arthritis is seen frequently in patients with anti-CCP antibodies, including other inflammatory diseases in the differential diagnosis is recommended.