A time-resolved immunofluorometric assay of autoantibodies to double-stranded DNA

A time-resolved immunofluorometric assay (TRIFMA) of autoantibodies to double-stranded DNA (dsDNA) is described. Biotinylated DNA was bound to the polystyrene solid phase coated with streptavidin. F(ab1')2 fragments from antibodies raised in rabbits to human IgG were labelled with Eu3+, and used in the assay to label the bound autoantibodies to dsDNA. The measuring range covers three decades. The proposed assay has good analytical properties. For calibration the First International Standard for antibodies to double-stranded DNA Wo/80 was used. The 97.5th percentile in normal persons is 20 kIU/l. Comparison of the TRIFMA and the Farr-assay in the analysis of 56 sera from 20 patients with systemic lupus erythematosus or lupus-like disease, 13 with other autoimmune diseases, and 10 blood-bank donors indicates a high degree of concordance (Kendall's tau = 0.56, p < 0.001). Further evaluation in 102 patients with systemic lupus erythematosus, lupus-like disease and other autoimmune diseases shows that sensitivity for active classical systemic lupus erythematosus is adequate, and specificity is excellent.