Radioactive iodine scan


Close oral contemporaneous use of iodinated contrast with CT scans and radioactive iodine scanning should be avoided because of false negative results.

The test is performed after TSH stimulation, either by thyroid hormone withdrawal or by administration of human recombinant TSH.

PET scans can localize sites of metastases and demonstrate radioactive iodine resistance, as thyroid carcinomas that have low iodine uptake have higher glucose metabolism and are more likely to be positive on PET scans.

Radioactive iodine has little or no therapeutic effect on PET scan positive tumors and tumors that concentrate radioactive iodine are not likely to be active on PET scan.

FDG avidity is the most practical and reproducible definition of radioactive iodine resistance disease in thyroid cancer with a median sensitivity and specificity of 77% in 78%, respectively.

A negative pregnancy test should be obtained in women of childbearing age 48 hours or less prior to such a scan.

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