Thyroid Iodine Determined by X-Ray Spectrophotometry

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Abstract
The amount of thyroid iodine was determined in vivo by x-ray spectrophotometry in 19 cases of thyrotoxicosis, 15 nontoxic goiters and 18 controls. The mean iodine values for the 3 groups were 12.5, 20.4 and 12.9 mg, respectively, but large individual variations were found. The radioiodine uptake test was also performed on all the subjects, and their PBI values were determined. The results obtained for cases of nontoxic goiter show that, on an average, there is an increase in both the thyroid uptake of radioiodine and the stored iodine. Although the causes of these changes remain obscure, it seems likely that there is an increased demand for iodine in nontoxic goiter. In thyrotoxic subjects the specific activity of radioiodine 7 days after the administration of radioiodine was considerably higher in the plasma than in the thyroid. In the metabolism of thyroid iodine occurring in thyrotoxicosis, there appears to be an important pathologic change whereby the iodine taken up from the blood stream and synthesized to thyroid hormone is rapidly secreted again without entering the main thyroid iodine pool.