Abstract: Objective:To detect plasma D-dimer levels in patients with autoimmune diseases (AID) and study the clinical significance.Methods:The levels of plasma D-dimer in 214 patients with AID were detected by latex particle enhanced immunoturbidimetric assay.The AID patients were classified with Classfication Standard of American Rheumatism Association,77 patients with rheumatoid arthritis(RA),69 patients with systemic lupus erythematosus(SLE),35 patients with idiopathic thrombocytopenic purpura,15 patients with systemic sclerosis and 18 patients with primary sjogren's syndrome were selected.The levels of plasma D-dimer were observed during the different activities of these diseases,before and after treatment,the correlations of D-dimer levels with blood routine and biochemical indexes were also analyzed.Results:Plasma D-dimer level in RA patients was significantly higher than that in the other 4 groups (P<0.05 to P<0.01).During the time of the disease with high activity,D-dimer levels in RA and SLE patients were both significantly higher than those of the disease with low activity(P<0.01).After therapy,D-dimer levels in RA and SLE patients were significantly lower than that during and before therapy(P<0.05 to P<0.01).In RA group,the rheumatoid factor was positively correlated with the level of D-dimer(P<0.01).In SLE group,D-dimer level was positively correlated with plasma uric acid level(P<0.01),negatively correlated with the numbers of red blood cell and platelet(P<0.01).Conclusions:In the five common type AID patients,the level of plasma D-dimer in RA patients was highest,following in SLE,and the level of D-dimer was closely associated with disease activity index and treatment phases.The findings suggested plasma D-dimer level may use as a clinical reference index of the disease activity and curative effectiveness in RA and SLE patients.