Clinical evaluation of a new automated anti-dsDNA fluorescent immunoassay

The measurement of antidoublestranded DNA (antidsDNA) antibodies is a useful tool for the diagnosis and the followup of systemic lupus erythematosus (SLE). AntidsDNA antibodies are involved in the pathogenesis of lupus nephritis and they are, specially the highavidity antibodies, the most specific antibodies associated with SLE nephritis and active SLE. The aim of the present study was to assess the clinical utility of an enzymelinked immunosorbent assay (ELISA) that utilizes a circular doublestranded plasmid DNA as a nucleic acid source, adapted to an automated fluorescence immunoassay (EliA(TM) dsDNA, Pharmacia, Freiburg, Germany). Also, we compared this method with other immunoassays used in clinical laboratories. We have measured antidsDNA antibodies in the serum of 179 patients with a positive result for antinuclear antibodies (ANA). Seventy six sera were from SLE patients (14 men and 62 women), and the other 103 sera (from 20 men and 83 women) constituted the control group. This latter group includes nine Sjogrens syndrome patients, six patients with rheumatoid arthritis and 88 with various other diseases, including connective tissue diseases (n=34), hepatopathies (n=17; 11 primary biliary cirrhosis and 6 autoimmune hepatitis), and 37 patients with nonautoimmune diseases (viral hepatitis, renal disease, diabetes, exanthema and hypertension). Methods used were EliA dsDNA (Pharmacia, Germany), Varelisa dsDNA (Pharmacia, Germany), Farr (Amersham, UK) and Chritidia luciliae immunofluorescence test (VitroImmun, Germany). We assessed sensitivity, specificity, positive predictive value and negative predictive value in the clinical study, and kappa index and scatter plots in the comparative study. The results show a low concordance between methods (kappa<0.6). The evaluated EliA method shows a very good specificity for SLE (93.2%) and a good sensitivity for active SLE (70.8%).