Background: Rheumatoid arthritis is one of the most common autoimmune diseases. Early diagnosis can prevent side effects and disability. Anti-cyclic citrullinated peptide antibody is a specific marker to diagnose rheumatoid arthritis. This study was carried out to evaluate the efficacy of anti-cyclic citrullinated peptide in comparison with rheumatoid factor in rheumatoid arthritis patients referred to Behshti Hospital of Kashan city during 2006-7.

Materials and Methods: This diagnostic value study was done on 98 randomly selected rheumatoid arthritis patients and 75 patients with other rheumatic diseases. In this study rheumatoid factor titer>35 IU/ml and anti-cyclic citrullinated peptide>6.25 IU/ml were considered positive.

Results: Anti-cyclic citrullinated peptide compared to rheumatoid factor had a higher sensitivity (73.5% vs. 69.4%), specificity (88% vs. 84%), positive predictive value (88.9% vs. 85%), and negative predictive value (71.7% vs. 67.7%) for rheumatoid arthritis. The use of rheumatoid factor and anti-cyclic citrullinated peptide test together increased the specificity and positive predictive value for diagnosis of rheumatoid arthritis to 93.3% and 92.4%, respectively. The mean anti-cyclic citrullinated peptide showed a significant difference in Rheumatoid arthritis (46.8 IU/ml( in comparison to non rheumatoid arthritis patients (5.3 IU/ml).

Conclusion: Anti-cyclic citrullinated peptide had a better diagnostic value when compared to rheumatoid factor for detection of rheumatoid arthritis. Also combined use of rheumatoid factor and anti-cyclic citrullinated peptide had a higher specificity and positive predictive value than each alone for the diagnosis of rheumatoid arthritis.