New biomarkers for rheumatoid arthritis

Rheumatoid factor (RF) has been commonly used as a biomarker of rheumatoid arthritis (RA). It is important to diagnose RA early and to prevent joint destruction before irreversible damage occurs. For this purpose, several new biomarkers, such as anti-cyclic citrullinated peptide antibody (anti-CCP) and matrix metalloproteinase-3 (MMP-3), have become available for both the diagnosis and prognosis of RA. RF showed a tolerable sensitivity of 68.5% for RA, but low specificity of 77.1% for patients with other rheumatic diseases. Anti-agalactosyl IgG antibodies (CARF) showed a slightly higher sensitivity of 73.9%, but specificity as low as that for RF. In contrast, anti-CCP demonstrated high sensitivity of 76.1% and marked specificity of 92.4% for patients with other rheumatic diseases. Anti-CCP was significantly superior to other biomarkers on receiver-operating characteristic curve (ROC) analysis. Moreover, meta-analysis revealed that the pooled sensitivity and specificity were 67% and 95% for anti-CCP, and 69% and 85% for RF, respectively, and that anti-CCP was more specific than RF for diagnosing RA. On the other hand, MMP-3 has been suggested to be a prognostic biomarker as well as an evaluative biomarker for RA. We next examined if the diagnostic accuracy of early RA is improved by combining these biomarkers. The specificity of RF was not as high as anti-CCP but rose to 92% when combined with MMP-3. Thus, we concluded that anti-CCP is superior to other biomarkers in terms of diagnostic accuracy, and that these combined assays are useful in the early diagnosis of RA.