New diagnostic tests for rheumatoid arthritis

Rheumatoid factor(RF) is one item in the classification criteria for rheumatoid arthritis(RA), with a tolerable sensitivity of 69.3% for RA but low specificity against other rheumatic diseases(76.4%). Anti-agalactosyl IgG antibody(CARF) showed a slightly higher sensitivity(72.0%) but the specificity was even lower(67.9%). Anti-cyclic citrullinated peptide antibody(anti-CCP), a new diagnostic test for RA, demonstrated higher sensitivity(76.0%) and specificity(91.5%), and the ROC analysis revealed the marked superiority of anti-CCP to other markers(i.e. RF, CARF, and IgG-RF). Matrix metalloproteinase-3 (MMP-3) showed a significantly positive correlation with CRP, suggesting it might be more useful for evaluation of RA activity and prediction of the prognosis of joint destruction. On the contrary, two combination assays, "MMP-3 or CARF" and "MMP-3 or anti-CCP", showed the highest sensitivity(86.7%) for RA. Similarly, in early RA the sensitivities of CARF, MMP-3 and anti-CCP were lower than in RA(66.7%, 66.7% and 58.3%, respectively), but the sensitivities of combination assays "MMP-3 or CARF" and "MMP-3 or anti-CCP" were 91.7% and 83.3%, respectively. Thus, we concluded that these combination assays are useful in the diagnosis of RA and detection of early RA.