INTRODUCTION: Rheumatoid arthritis (RA) is one of the most common autoimmune rheumatic diseases, but a specific and reproducible test for its diagnosis is still lacking. OBJECTIVES: To evaluate the diagnostic efficiency of a new commercial ELISA kit in detecting anti-cyclic citrullinated peptide antibodies (anti-CCP) for the diagnosis of RA. METHODS: Anti-CCP antibodies and rheumatoid factor (RF) were determined in the serum of 486 patients: 100 patients with RA and 386 controls, including healthy subjects, patients with other non-rheumatic and rheumatic disease, as well as patients with infections disease. Comparative evaluation of diagnostic performance of anti-CCP and RF was done by calculation the several diagnostic indexes and construction of the ROC (receiver operator characteristic) curve. Statistical analysis included chi-square, Fisher exact, and Mann-Whitney's test. RESULTS: At cutoff of 25 UI/ml, anti-CCP showed sensitivity of 68% (95% CI, 57,8-76,8%), specificity of 97,7% (95% CI, 95,5-98,8%), positive predictive value (VPP) of 88,3% (95% CI, 78,5-94,2%), negative predictive value (VPN) of 92,2% (95% CI, 89-94,5%) and likelihood ratios (LR) of 29,2% (95% CI, 15,1-56,4%). Anti-CCP-positive RA patients had a mean antibody concentration of 920,7 UI/ml (range, 70,5-2000 UI/ml). Anti-CCP-positive non-RA patients had a mean antibody concentration of 38,7 UI/ml (range, 29,5-47, 4 UI/ml). The diagnostic performance of anti-CCP, as estimated by the ROC curve, was superior to that of RF. RF had a higher sensitivity (91%) and a lower specificity (78,8%) than anti-CCP. When the two antibodies were used together, specificity was 99,5%. CONCLUSION: The anti-CCP testing presented the best diagnostic performance for RA and was the most specific test. It may be useful if performance concomitantly with RF in the diagnostic difficulty.
rheumatoid arthritis; diagnostic; autoantibodies; anti-cyclic citrullinated peptide
