Reproducibility studies for anti-DNA antibody detection in systemic lupus erythematosus and related diseases. FIAX fluorometric immunoassay and Farr radioimmunoassay.

We compared the FIAX fluorometric immunoassay for antiDNA antibodies with a Farr radio-immunoassay. Neither was precise; coefficients of variation usually exceeded 10%. The 2 assays correlated well (r = 0.87). Both were almost completely specific for numbers of sera with elevated antiDNA preferable to the Farr assay and probably to all other antiDNA assays currently used in clinical situations, although its reproducibility needs improvement.