A Simple Method for Estimating Serum Thyroxine Concentration in Thyroid Disease and Iodine-Treated Patients

A simple method for estimating serum thyroxine (T4) levels has been developed. In this method T4 is extracted from serum and purified by solvent distribution for quantitative measurement by the classic ceric reduction method. Chromatography and combustion are not required. The method is very reliable in the evaluation of thyroid function. In 124 euthyroid control patients the average serum thyroxine iodine (T4I) level was 4.7 μg/100 ml (95 % confidence limit: 3.1–7.3 μg/100 ml). In 27 hypothyroid patients all T4I values were less than 3.1 μg/100 ml, while they were greater than 7.3 μg/100 ml in 29 hyperthyroid patients. This method has a considerable advantage over PBI and BEI methods in that commonly used iodinated materials rarely interfere with the determination of T4I. In a total of 119 euthyroid patients who had elevated PBI values after receiving iodide (n = 30), Hypaque (n = 30), Pantopaque (n=30), Telepaque (n = 26), or Dionosil (n = 3), all but 3 patients had normal serum T4I levels.