Mechanism of radioactive iodine uptake depression following intravenous urography.

The radioactive iodine (RAI) uptake examination is a standard test for the evaluation of thyroid diseases. For many years it has been known that the results of the RAI are depressed following administration of iodinated contrast media, such as that used for intravenous urography (Williams, 1968; Beierwates, 1956; Slingerland, 1957). The mechanism of this depression is not well documented. It is presumably due to inorganic iodide since it is only inorganic iodide that can be extracted from the blood by the thyroid gland. To study this problem we measured inorganic iodide in bottled contrast media.