IMPROVED RADIOASSAY FOR HUMAN ANTITHYROGLOBULIN

Human antithyroglobulin (anti-HTg) in serum and tissue cultures can be assayed by coprecipitation with 125I-labeled human thyroglobulin (HTg). Coprecipitation of the antibody from different sera gives roughly parallel curves, so that a standard serum can be used for quantitation of other sera. By assessing the binding of 125I-labeled HTg in antigen excess the antibody content of the standard serum was estimated to be 0.14 ng anti-HTg per ml. Shortened incubation minimizes nonspecific binding of HTg to serum globulins and obviates preassay absorption of HTg. Radioassay for thyroglobulin antibodies in serum correlated with values obtained by solid-phase competitive-binding assay (SPCB). One unit in the assay corresponds to 0.014 unit by the latter assay and to 0.12 units of MRC Research Standard A. Serum thyroglobulin seriously interferes with SPCB assay, giving what appears to be positive results for anti-HTg where none is detected with the assay. Values for anti-HTg are depressed by serum HTg but only in the presence of very high concentrations in serum.