METHOD FOR INCREASING THE ACCURACY OF THE RADIOIODINE UPTAKE AS A TEST FOR THYROID FUNCTION BY THE USE OF DESICCATED THYROID*†

THE accumulation of radioiodine by the thyroid has become well established as one of the most sensitive and reliable tests of thyroid function. Nevertheless, there are some patients seen at most clinics in whom it is impossible to make an unequivocal diagnosis with this procedure. These usually fall into three groups: a) patients with many signs and symptoms of hyperthyroidism but with thyroidal radioiodine uptake within the normal range; b) patients with little or no clinical evidence of hyperthyroidism but with I131 accumulation above the normal range; c) patients with or without symptoms, who have an equivocal, “borderline” uptake ranging between the euthyroid and hyperthyroid levels. A fourth group of patients who are clinically euthyroid but have a subnormal uptake are not included in this consideration, since such a discrepancy is usually explained by saturation of the “iodine pool” of the body. It has been found that the daily administration of physiologic amounts of desiccated thyroid to euthyroid subjects will result in a suppression of their thyroidal radioiodine metabolism to levels seen in myxedema (1). The present study was designed to extend the observations of the effect of exogenous thyroid to include patients with simple goiter and those with hyperthyroidism. It was found that patients with simple goiter had approximately the same degree of thyroid suppression induced by an equivalent amount of exogenous thyroid hormone as did euthyroid patients without goiter. Thyrotoxic patients, on the other hand, required much larger amounts of thyroid to produce appreciable depression of their thyroidal radioiodine metabolism.