II. Some Applications of I131and Na24to Clinical Diagnoses

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Abstract
Several methods of measuring thyroid function using radio iodine have been published and are in use. They depend on the measurement either of the uptake by the thyroid gland or of the urinary excretion of I131 given to the patient. Several reviews on this subject have been published (Kelsey et al., 1949; Werner et al., 1949), and it is proposed to deal here only with a method which has been developed and used extensively in our Bristol Tracer Laboratories. In contrast to most other methods we injected only small doses (15 to 25 μc.) of carrier-free I131. The injections were given intravenously so that the measurement did not rely on constant absorption from the gastro-intestinal tract, and the I131 uptake of the thyroid area was recorded for about 1 hour, starting from the moment of completion of the injection. Measurements carried out later than this obviously give the resultant of the I131 uptake and the mobilisation of protein-bound I131 from the thyroid, and, therefore, a true measure of the iodine avidity of the thyroid can only be obtained during a short period after the injection. This avidity can be taken as the most clear-cut expression of the functional state. It seemed, moreover, that some relation between the iodine avidity of the thyroid and the urinary excretion of the iodine might define thyroid function uniquely.