Immunoassay of Thyroxine in Unextracted Human Serum

Abstract

A method for the immunoassay of thyroxine (T4) in unextracted human serum is presented. Thyroxine-binding antibody was obtained by immunization of a rabbit with bovine thyroglobulin. Sodium salicylate is used to block the binding of both labeled and unlabeled T4 to serum thyroxine-binding proteins. Bound and free labeled hormone are separated by adsorption to dextran-coated charcoal. The method is sufficiently sensitive to allow duplicate determinations at two dilutions using 20 μ1 of serum. The precision of the method is comparable to the competitive protein binding assay and there is excellent correlation between the estimation of T4 by these two methods (correlation coefficient, 0.97) in all clinical states.