Reevaluation of the ammonium sulfate assay for DNA antibody.

The ammonium sulfate assay has recently come under criticism for alleged inability to detect low avidity antibody to DNA. The results of this study verify that a small percentage of antibody binding is not detected when this assay is performed under the conditions generally used. However, when the values obtained by the ammonium sulfate assay were compared to those obtained by other assays on sera of known avidity for DNA, it was concluded that ammonium sulfate does not selectively dissociate low avidity antibody from DNA. Conditions of incubation buffer and duration, pH, concentration of reactants, and molecular weight of the antigen are described for optimal detection of DNA antibody by the ammonium sulfate assay.