Topics on immunological tests for rheumatoid arthritis

To prevent joint destruction, it is important to diagnose RA early and to speculate the prognosis. Several new laboratory tests have been developed for this purpose. In addition to rheumatoid factor (RF), IgG-RF, anti-agalactosyl IgG antibodies (CARF), and matrix metalloproteinase 3 (MMP-3) have become available as diagnostic tests for RA. Among them, anti-cyclic citrullinated peptide antibodies (anti-CCP antibodies) have the sensitivity and specificity of 81.0% and 92.4%, respectively, which are superior to other laboratory tests by ROC analysis. Moreover, the specificity of anti-CCP antibodies to diagnose early RA was much higher than that of RF, although the sensitivity of CARF was slightly high compared with that of RF. In contrast, MMP-3 is thought to be an evaluative test for the activity of RA because a significant correlation was found between MMP-3 and CRP, but MMP-3 has a possibility as a prognostic test to know the joint damage of RA. We have shown that the progression of joint damage (Sharp score) was faster in MMP-3-positive patients than negative patients. Anti-CCP antibodies was also reported to associate with the progression of joint damage and may be used also as a prognostic test. We next examined how efficiently was the diagnosis of RA made by combining these laboratory tests. Although anti-CCP antibodies are highly specific to RA, the specificity of RF was not so high but became up to 92% when combined with MMP-3. In order to diagnose RA efficiently, we may firstly examine RF, next MMP-3 if RF is positive, and anti-CCP antibodies if RF is negative.