Conventional and dual competitive binding analyses of thyroxine using the Thyopac-4 kit.

A simple method is described for the simultaneous determinations of thyroxine and the effective thyroxine ratio (ETR) using a single kit of Thyopac-4. Thyopac ETR values obtained were 1.00 +/- 0.03 for normal subjects; 1.22 +/- 0.11 for hyperthyroid; 0.87 +/- 0.04 for hypothyroid; and 1.02 +/- 0.05 for pregnant women. Cases with TBG deficiency and the nephrotic syndrome indicated normal values. The value (x) was correlated significantly (gamma = + 0.961) with the free Thyopac index (y), representing a regression equation of y = 71.7x(2) - 88.4x + 24.2. Thyopac ETR was shown to be useful in differentiating normal thyroid states from abnormal, irrespective of changes in T(4)-binding globulin (TBG). Further, the T(4) value obtained simultaneously made it possible to detect changes in the TBG level by noting an inconsistent value for the effective thyroxine ratio.