Horm Metab Res 1980; 12(11): 611-614
DOI: 10.1055/s-2007-999212
© Georg Thieme Verlag, Stuttgart · New York

Direct Measurement of Free Thyroxine in Patients with T3-Toxicosis

T. Lin, H. R. Nankin
  • Medical Service, William Jennings Bryan Dorn Veterans' Hospital and Department of Medicine University of South Carolina School of Medicine Columbia, South Carolina, U.S.A.
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Publication Date:
22 April 2008 (online)


Circulating levels of free thyroxine were directly measured using a new kinetic radioimmunoassay system. Free thyroxine was abnormally elevated in: 1) each of eleven hyperthyroid individuals having elevated concentrations of thyroxine and triiodothyronine; and 2) all five hyperthyroid subjects who had normal circulating levels of thyroxine but elevated concentrations of triiodothyronine (T3-toxicosis). Using this assay system, free thyroxine appears to be elevated in all hyperthyroid individuals.