Diagnostic value of anti-Sa and anticitrullinated protein antibodies in rheumatoid arthritis.

Objective: To determine the diagnostic value of anticitrullinated protein antibodies, second generation (ACPA2), by electrochemiluminescent immunoassay (ECLIA) and anti-Sa by ELISA in a large cohort of Chinese patients with early rheumatoid arthritis (RA).

Methods: One hundred ninety-eight patients with early RA (< 1 yr duration), 112 with other rheumatic diseases, and 60 healthy individuals were studied.

Results: The combination of anti-Sa and ACPA2 positivity had the highest specificity (99.42%), but it had a rather low sensitivity (50.0%). The combination of anti-rheumatoid factor (RF) and ACPA2 showed the highest sensitivity (80.30%), with specificity of 95.93%. The mean titer of ACPA2 and RF was significantly higher in the anti-Sa-positive group compared to the negative group (ACPA2, p <0.001; RF, p = 0.007). The 28-joint Disease Activity Scores of the anti-Sa-positive patients were significantly higher than those of the negative group (p = 0.01). The anti-Sa had no significant correlation with age, sex, antinuclear antibody, SSA, SSB, erythrocyte sedimentation rate, C-reactive protein, immunoglobulin A (IgA), IgG, IgM, C3, and C4.

Conclusion: Our results come from a newly developed ECLIA for detection of ACPA2 and the anti-Sa-antibody-based ELISA system. The combined application of ACPA2 and anti-Sa tests can improve the laboratory diagnosis of early RA.