A simple and reproducible method for the estimation of triiodothyronine uptake (thyroxine binding index) using a new adsorbent.

A simple, rapid and reproducible method for the determination of triiodothyronine uptake using heat-treated wheat flour (TWF) as adsorbent is described. Three ml of TWF suspension in barbital buffer containing 125I triiodothyronine is added to 0.1 ml of serum sample in a plastic tube. The mixture is shaken for 30 seconds and is left to settle for 12 minutes or alternatively is centrifuged for one minute at 600 X g. The 1.0 ml of supernatant is transferred to another tube for counting. This method is virtually time and temperature independent. The effects of altering the concentration of 125I triiodothyronine and TWF are reported. Within-run precision has been estimated for normal (C.V. 1.2), high (C.V. 1.2) and low (C.V. 1.8) ranges. Estimation of between -run precision gave similar results. Comparison of results obtained by this method and by Thyopac-3 reagent kit (Radiochemical Centre, Amersham, England) shows good correlation for Thyopac-3 values about 105, while for values below 105 the present method gives lower values than Thyopac-3.