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Evaluation of new kits for the assessment in vitro of thyroid function by determination of serum total thyroxine, free TBG capacity, and free thyroxine index using Sephadex G-25 and 125I-labelled triiodothyronine and thyroxine
  1. P. J. N. Howorth,
  2. C. G. McKerron
  1. Department of Chemical Pathology, King's College Hospital Medical School, London
  2. Department of Medicine, King's College Hospital Medical School, London


    A trial was carried out on 134 patients of new kits (Ames Co) using columns of Sephadex G-25 for the determination of serum total thyroxine (Tetralute test) and for the indirect estimation of serum free thyroxine-binding globulin capacity (Trilute test). Both new methods were quicker and easier than the reference resin methods and of similar precision. The two measurements when combined to give a free thyroxine index (Trilute-Tetralute-FTI) increased further the diagnostic discrimination and usefulness of the tests.

    The method for the determination of serum thyroxine can be modified to give a direct estimate of serum free thyroxine, expressed as a free thyroxine index. This new single-column technique, called the `single-column free thyroxine index', gave a good correlation with clinical thyroid status in a preliminary trial of 45 patients.

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