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Radioactive Iodine Uptake Test

A radioactive iodine uptake (RAIU) test uses a radioactive tracer and a special probe to measure how much tracer the thyroid gland camera.gif absorbs from the blood. The test can show how much tracer is absorbed by the thyroid gland. The RAIU test often is done along with a thyroid scan, which shows if the tracer is evenly spread in the gland. This helps your doctor know if the thyroid gland is working properly. The radioactive tracer commonly used in this test is iodine.

A radioactive iodine uptake test is done to find problems with how the thyroid gland works, such as hyperthyroidism.

Why It Is Done

A radioactive iodine uptake (RAIU) test is done to:

  • Find the cause of an overactive thyroid gland (hyperthyroidism).
  • Plan treatment for hyperthyroidism.
  • Plan treatment for patients who have had thyroid cancer surgery.

How To Prepare

Tell your doctor if you:

  • Take any medicines regularly. Be sure your doctor knows the names and doses of all your medicines. Your doctor will instruct you if and when you need to stop taking any of the following medicines that can change the RAIU test results:
    • Thyroid hormones
    • Antithyroid medicines
    • Medicines or supplements that contain iodine, such as iodized salt, kelp, cough syrups, multivitamins, or the heart medicine amiodarone (such as Cordarone or Pacerone)
  • Are allergic to any medicines, such as iodine. But even if you are allergic to iodine, you will likely be able to have this test because the amount used in the tracer is so small that your chance of an allergic reaction is very low.
  • Have ever had a serious allergic reaction (anaphylaxis) from any substance, such as the venom from a bee sting or from eating shellfish.
  • Have had any test using radioactive materials or iodine dye, such as a CT scan, 4 weeks before the RAIU test. These other tests may change the results of the RAIU test.
  • Are or might be pregnant.
  • Are breast-feeding.

Before an RAIU test, blood tests may be done to measure the amount of thyroid hormones (TSH, T3, and T4) in your blood.

To prepare for an RAIU test:

  • Follow your doctor's instructions about not eating before the test. Most often, you will need to stop eating 8 hours before the test.
  • Tell your doctor about all of the medicines, vitamins, and supplements you are taking. You may need to stop taking some medicines or supplements for a while before the test.

Your doctor may ask you to eat a low-iodine diet.

For an RAIU, you will swallow a dose of radioactive iodine. Iodine can be taken as a capsule or a fluid 4 to 24 hours before the test. Iodine has little or no taste.

Just before the test, you will remove your dentures (if you wear them) and all jewelry or metal objects from around your neck and upper body.

You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

WebMD Medical Reference from Healthwise

Last Updated: April 29, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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