Abstract
With the wide usage of the thyroidal radioiodine uptake test in the evaluation of thyroid function, it is important to define some of the limitations and sources of error in this procedure. One common problem is the artifactual lowering of the thyroidal radioiodine uptake which follows administration of various iodine-containing compounds. A number of studies on the effect of some cholecystographic, pyelographic and bronchographic contrast media and stable iodine on the thyroidal 131-I uptake has resulted in conflicting information. Moreover, there have been no accurate reports concerning the effect of iodine-containing compounds on the thyroidal uptake of radioactive iodine except for seaweeds which are commonly taken as food in Japan.
In this study the duration of interfering effect of various iodine-containing compounds on the thyroidal 24-hr. 131-I uptake was determined. The iodine-containing compounds investigated were potassium iodide, Maryngin-M, Entero-Vioform (Iodochloroxy-Quinoline), Telepaque (Iodopanoic acid, for oral cholecystography), Biloptin (for oral cholecystography), Biligrafin (Iodipamide Sodium, for venous cholecystography), Urografin (Diatorizoate Sodium, for intravenous pyelography, angiography, arthrography, fistelography and discography), Moljodol (for hysterosalpingography and myelography), Endografin (for hysterosalpingography) and Myodil (for myelography and fistelography).
The subjects employed were 180 euthyroid patients and 5 cases of hyperthy-roidism without any hepatocholecystic and renal dysfunction. None had any indication of thyroid abnormality and there was no history of taking interfering medicinal or chemical agents in euthyroid subjects. Prior to the uptake test, intake of any form of iodine was restricted for 7 days and the uptake was measured before and after administration of a drug. Follow-up studies were performed at varying intervals following administration of the iodine-containing compounds. After the basic study, all data for radio-iodine content in the thyroid were corrected for the amount of 131-I present in the thyroid just before each new test dose. To further minimize the error resulting from the thyroid residual of 131-I, successive test doses were made progressively larger.
In the euthyroid subjects given 1 to 1000 mg of potassium iodide orally three times a day, it was observed that the uptake recovered within 48 hrs with 5 mg, within 72 hrs with 100 mg and within 4 days with 1000 mg of potassium iodide, respectively, although no inhibition was observed with 1 mg. In 9 patients given 3 gm of Marygin-M (I : 2.7 mg) three times a day, the uptake returned to the preadministration level about 2 days after administration. In 8 patients given 1.5 gm of Entero-Vioform (I : 579 mg) three times a day, the uptake returned to the previous level about 7 days after administration. In 25 patients given 6 tables (3.0 gm) of Telepaque (I : 1.98 gm) in a single dose, the uptake recovered within normal range 3 weeks after administration, while with 6 tables (3.0 gm) of Biloptin (I : 1.86 gm) at recovered 2 weeks after administration. In all 5 cases with intravenous administration of 20 ml of 30% (I : 3.0 gm) and 50% (I : 5.0 gm) of Bili-grafin, the uptake returned to normal range about one week after daministration, respectively. In all 7 cases with intravenous and intraarterial administration of 20 and 30 ml of 76% Urografin (I : 7.4 and 11.1 gm), the uptake recovered to the preadministration level 4 days after administration, respectively. In all 3 patients who underwent arthrography (2-8 ml of 76% Urografin, I : 0.74-2.96 gm), the uptake returned to normal range about 38 days after administration. In 2 patients who underwent fistelography (5-15 ml of 76% Urografin, I : 1.05-5.55 gm), the uptake returned to normal range 23 days after administration,
