Improved Method for the Measurement of Serum Thyroxine

Abstract

Methodology for the measurement of thyroxine in unextracted human serum is described. Antibodies were prepared by immunization of rabbits with thyroxine-human serum albumin (T₄-HSA) conjugates. Bound and free labeled hormones are separated using the double antibody technique. The validity of the assay has been demonstrated by the excellent recovery of exogenous T₄ added to various serum samples and by production of a curve obtained by various dilutions of a hyperthyroid serum which is parallel to the standard curve. Radioimmunoassay T₄ values ranged from 4.5 to 12.0 μg/100 ml in 172 euthyroid patients. In all clinical states, serum T₄ values obtained by radioimmunoassay afforded excellent agreement (correlation coefficient, 0.95) with those obtained by competitive protein binding assay. Advantages of the method over commercially available radioimmunoassay kits or the competitive protein binding assay are outlined.