A simple technique using `dialysable' thyroxine for assessment of thyroid status

Abstract

SYNOPSIS A simple method for assessing thyroid status is described in which the percentage of radioactive thyroxine dialysed through a semi-permeable membrane between plasma samples is estimated. The results compare favourably with other tests in vitro.Two factors which influence thyroid status are the plasma content of thyroid hormone (mainly thyroxine) and the binding capacity of the thyroxinebinding protein; these dispose the quantity of thyroxine available to the tissues. Unfortunately neither protein-bound iodine or plasma thyroxine (Ekins, 1960) nor thyroxine-binding protein capacity (Robbins, 1956) are very simple to estimate as a routine. The quantity of thyroxine not bound to protein, or available, is too small to be estimated directly. By the addition of a small trace of 1311-labelled thyroxine to plasma it is possible to estimate the proportion of total thyroxine which is free, or available, by dialysis from plasma to buffer solution (Sterling and Hegedus, 1962) and this has been found to give a good indication of thyroid status. The technique is, however, somewhat exacting since the proportion of thyroxine 1311 which is dialysable from plasma to buffer is exceedingly small, owing to the high affinity of thyroxine-binding protein for thyroxine. It is easier to estimate the proportion of a trace of 1311 thyroxine which is dialysable in a given time across a semi-permeable membrane separating two plasma samples (Christensen, 1959

Dialysable thyroxine index in the assessment of thyroid status

“…1 SIXTEEN-HOUR DIALYSABLE THYROXINE The method has been described (Gimlette, 1964). In outline, it consists in the estimation of the percentage of a tracer of 1131 thyroxine added to the plasma under investigation which is dialysed, during 16 hours at 37°C., out of a small cellophane bag immersed in a sample of the same plasma in a test tube.…”

“…Direct estimation of this concentration, which is of the order 0-1 % of total thyroxine, has not so far been possible. However, by indirect methods using 1131 thyronines as tracers, free thyroxine or the relative concentration of free thyroxine have been estimated (Robbins and Rall, 1957;Sterling and Hegedus, 1962;Osorio, Jackson, Gartside, and Goolden, 1962;Christensen, 1959).A simple technique for estimating dialysable thyroxine has been described (Gimlette, 1964) and in the present study this has been combined with the estimation of plasma thyroxine (Ekins, 1960), the product giving a relative measure of free or available thyroxine, the dialysable thyroxine index. …”

“…A simple technique for estimating dialysable thyroxine has been described (Gimlette, 1964) and in the present study this has been combined with the estimation of plasma thyroxine (Ekins, 1960), the product giving a relative measure of free or available thyroxine, the dialysable thyroxine index.…”