Summary
The direct estimation of serum thyroxine iodine (T4I) and the uptake of125I labelled thyroxine from serum by anion exchange resin (R.U.R.) can both be used independently to assess thyroid status. The results from these two tests can be combined to give a free thyroxine index (F.T.I.) which is believed to be proportional to the concentration of free thyroxine in the serum.
A comparison has been made between the diagnostic accuracy of the T4I, R.U.R. and F.T.I. as done by the above method, carried out on a series of 137 patients who fall into five diagnostic categories, euthyroid, hypothyroid, hyperthyroid, pregnant and nephrotic. It was found that the amended F.T.I. gives better agreement with clinical status than either the T4I or R.U.R. alone.
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Smyth, P.P.A., O’Donovan, D.K. The “free thyroxine index”. I. J. Med. Sc. 2, 515–521 (1969). https://doi.org/10.1007/BF02955461
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DOI: https://doi.org/10.1007/BF02955461