The Purification Of Sa Antigen And The Diagnostic Value Of Anti-Sa Antibody In Patients With Rheumatoid Arthritis

Objectives To explore the diagnostic value of anti-Sa auto-antibody in patients with rheumatoid arthritis (RA), and to purify Sa antigen.Methods There were 1088 sera in patients with RA (n=517) and with non-RA (n=571). Anti-Sa antibody was detected using immunoblot test (IBT) and Sa antigen was further purified using two ways of ion exchange chromatography and affinity chromatography.Results The sensitivity of anti-Sa was 37.9﹪ with high specificity(94.7﹪) in RA and 40.7﹪ sera of the recent-onset RA group were positive of anti-Sa. The RA patients with anti-Sa were statistically different from the patients without this antibody in morning stiffness and the counts of joints suffered. The positive rate of anti-Sa was 38.7﹪ in RA patients without rheumatoid factor(RF).There were statistical correlations in anti-CCP, RF, antiperinuclear factor (APF) and antikeratin antibody (AKA), but there were no statistical correlations in anti-Sa, anti-CCP and other RA-related antibodies. Anti-Sa combined with other antibodies using serial tests, the specificity for the diagnoses of RA was closed to 100﹪,and using parallel tests, the sensitivity was 88.6﹪and the area under the ROC curve was 0.901.Compared with crude antigen, the counts of protein bands of purified antigen were decreased and the band of Sa antigen was gathered.Conclusions The specificity of anti-Sa was highest with modest sensitivity in RA, and the detection of anti-Sa helps for early diagnosis of RA,and diagnose RA absent of RF. Anti-Sa might be associated with the severity of disease. There were no statistical correlations in anti-Sa and other RA-related antibodies in RA. The combination of anti-Sa and other antibodies helps increase the diagnostic value of anti-Sa in patients with RA. Improving the condition of the detection could increase the sensitivity of the test. Purified antigen could increase the accuracy of the diagnoses.