A New and Simple Method for the Determination of Thyroxine in Serum

Abstract

A new and simple method for measurement of serum T4 is introduced in which a modified I131 -T3 resin sponge uptake is used. Unlike the conventional I131-T3 resin sponge uptake, this new method can measure T4 concentration in the serum without regard to the amount of T4 binding protein in the serum sample. After 2 ml of the serum sample has been deproteinized, the standard stock serum is added to the free T 4 Then the I131 -T3 resin sponge uptake method is applied to this mixture. The T4 content of the serum sample is measured using the standard calibration curve of I 131 -T3 resin uptake values obtained using various concentrations of a T4 solution. The values for T 4- iodine ( [mu] g/100 ml) in various groups of diseases were: hypothyroidism, 2.3[plus or minus]0.70 (mean + SD); euthyroid subjects, 5.7[plus or minus] 1. 08; hyperthyroidism, 10.9[plus or minus] 2.30; pregnancy, 7. 0 [plus or minus] 1. 31; and nephrosis, 2.3[plus or minus] 0.94. Satisfactory reproducibility was observed by the duplicate determinations. These results proved that this method could be used as a routine clinical diagnostic test in place of the determination of PBI.