A comparison of the thyroidal plasma I131 clearance and the plasma protein-bound I131 tests for the diagnosis of hyperthyroidism.

Abstract

INTRODUCTION VARIOUS tests using radioactive iodine for the evaluation of thyroidal disorders have been described in numerous published reports (1–5). The most commonly employed have been the determinations of 24-hour thyroidal uptake (6, 7) or urinary excretion (8, 9) of radioiodine after an orally administered tracer dose. Although excretion measurements are technically easier, there is always uncertainty as to the completeness of the urine collection. The percentage uptake by the thyroid, therefore, has been more generally used. Although a reasonably good distinction between hypothyroidism and euthyroidism is thus obtained, it has become increasingly apparent that the wide overlap in values does not permit a definitive separation between normal and hyperthyroid states. Most of the tests which have been proposed recently are based on one of two different aspects of thyroid kinetics: the rate of thyroidal removal of iodide from the plasma (4, 10, 11), or the rate of appearance of organically bound iodine...