Fifteen cases of Graves' disease were studied before and after euthyroidism was achieved
with radio iodine treatment. In spite of the euthyroid status, the thyroidal 131I-uptake and PB1311 remained high. Measurements of the plasma inorganic iodine, the urinary iodine and
the absolute iodine uptake by the thyroid showed that the increased 131I uptake was not due to iodine deficiency, but mainly to faulty utilization of the
iodine trapped by the thyroid, probably because of an organification defect. The intrathyroidal
exchangeable iodine pool was decreased in the treated patients, and this could adequately
explain the high PB131I values in these cases. These results confirm the unreliability of in vivo studies
for assessing the euthyroid status of 131I-treated patients and provide an explanation for the discrepancy between clinical
status and in vivo iodine tests.
Iodine Metabolism - Graves' Disease - Thyrotoxicosis - Intrathyroidal Iodine Pool
- Radioiodine Treatment - Iodine Uptake - Iodine Utilization
