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Radioactive Iodine

My doctor has ordered a thyroid uptake/scan. What is this test, and how should I prepare for it?

The thyroid uptake/scan is a diagnostic test that is often used to determine the cause of hyperthyroidism (overactive thyroid). It is also sometimes used in the evaluation of goiter and thyroid nodules. A small, oral dose of radioactive iodine is taken, and then a scan is done after 4 hours, and then after 24 hours. If you are taking medication for hyperthyroidism, including methimazole (Tapazole) or propylthiouracil (PTU), you should stop taking it 5 days before the scan. Other medications can usually be continued; check with your doctor to be sure. Also, recent doses of iodine-containing iv contrast, such as the contrast used for CAT, or CT scans, can interfere with the thyroid scan, so let your doctor know if you have recently received a dose of iv contrast.

My doctor has ordered a radioactive iodine ablation treatment. What does this mean?

Radioactive iodine ablation refers to giving a dose of radioactive iodine sufficient to destroy some or all of the thyroid cells. It is often given for treatment of hyperthyroidism (overactive thyroid) or for treatment of thyroid cancer. If you are having radioactive iodine ablation done for treatment of hyperthyroidism, you should stop taking any antithyroid medications, such as methimazole (tapazole), or propylthiouracil (PTU), 5 days prior to the treatment, and can resume them 3-5 days after the ablation. If you are having ablation done for thyroid cancer, your doctor may ask you to stop taking thyroid hormone (levothyroxine, synthroid, levoxyl, or cytomel) 2-4 weeks prior to the ablation, or may ask you to take injections of thyrogen instead. You should be aware that after receiving radioactive iodine ablation, it is likely that your thyroid hormone levels will become low (hypothyroidism), and you may need to take thyroid hormone supplements for the rest of your life.

What side effects can I look for after radioactive iodine ablation treatment?

Most patients do not experience any side effects. Some patients may experience swelling or pain involving the salivary glands, or dry mouth. This is usually mild, and can be treated with ibuprofen for pain. Side effects are more common with higher doses of radioactive iodine that are given for thyroid cancer. Pregnant and breastfeeding women should not receive radioactive iodine, and you should not become pregnant within 6 months after receiving radioactive iodine ablation.

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