Diagnostic accuracy of the anti-citrulline antibody assay for rheumatoid arthritis

Background: Rheumatoid arthritis (RA) is the most common autoimmune rheumat ic disease, but specific and practicable tests for its diagnosis are lackin g. We evaluated the diagnostic accuracy of a new commercial ELISA in detect ing anti-cyclic citrullinated peptide (CCP) antibodies for the diagnosis of RA. Methods: Anti-CCP antibodies were determined in 330 serum samples: 98 from RA patients and 232 from controls, including patients with connective tissu e diseases, other rheumatic diseases, viral infections, Lyme disease, autoi mmune thyroiditis, cancer, and monoclonal gammopathy, and sex- and age-matc hed healthy subjects. Intra- and interassay CVs were 5-13% and 9-17%, respe ctively. Rheumatoid factor (RF) was also assayed in every sample,, and resu lts were compared to anti-CCP for sensitivity and specificity. Results: At a cutoff value of 50 units, sensitivity was 41% (confidence int erval, 31-50%) and specificity was 97.8% (95-100%). Anti-CCP-positive RA pa tients had a mean antibody concentration of 1100 units (range, 57-3419 unit s), and anti-CCP-negative RA patients and controls had mean values of 7.6 a nd 6.8 units, respectively (range, 1-39 units). The area under the ROC curv e was 0.71 (95% confidence interval, 0.63-0.78). RF had a higher sensitivit y (62%) and a lower specificity (84%) than anti-CCP. When the two antibodie s were used together, specificity was 99.6%. Conclusion: Anti-CCP antibody testing may be useful if performed concomitan tly with RF assay to diagnose patients with suspected early RA, (C) 2001 Am erican Association for Clinical Chemistry.