Diagnostic accuracy of currently available anti-double-stranded DNA antibody assays : an Italian multicentre study

OBJECTIVES: An Italian multicentre study was promoted in order to assess the accuracy of four anti-double-stranded DNA (dsDNA) antibody assays for SLE diagnosis and monitoring. METHODS: Two hundred and twenty-three patients with established SLE according to ACR classification criteria were enrolled from 9 centres. They included 59 patients at first evaluation (disease duration <12 months) and 164 with longer disease duration (median disease duration 120 months). The sera from 55 healthy subjects and 161 patients with rheumatic, infectious or neoplastic diseases were tested as controls. SLE activity was measured by ECLAM score. Anti-dsDNA antibodies were detected in serum by means of FarrzymeTM assay, fluoroenzymeimmunoassay (EliATM), Crithidia luciliae indirect immunofluorescence (CLIFT) or Farr radioimmunoassay (Farr). Cut-off values of quantitative assays were chosen by ROC curves analysis. Statistics were conducted by SPSS software package. RESULTS: Sensitivity for SLE diagnosis ranged between 66% with Farrzyme to 95% with Farr, with about 90% specificity for all the methods tested. Farrzyme assay was more specific than the others towards patients with non-SLE connective tissue disease. The four methods were moderately concordant and correlated among them, all showing a positive association with active disease, renal or haematologic involvement, and a negative association with central nervous system disease. Whatever the assay used, anti-dsDNA antibody levels correlated with disease activity with r correlation coefficients ranging from 0.336 to 0.425 (p