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Radioactive Iodine Uptake Test

How It Is Done

A radioactive iodine uptake (RAIU) test is done in the nuclear medicine section of a hospital's radiology department by a person trained in nuclear medicine (nuclear medicine technologist).

For this test, you will lie on your back with your head tipped backward and your neck extended. It is important to lie still during this test. A special machine is placed over your thyroid gland to measure the amount of tracer absorbed by the thyroid gland 4 to 6 hours after you took the iodine. This is not an X-ray machine—it is a scanner that detects the radiation given off by the tracer. The test takes about 10 minutes. Another scan is done again in 24 hours.

After an RAIU test, you can do your regular activities. But you will be asked to take special precautions when you urinate. This is because your body gets rid of the radioactive tracer through your urine. This takes about 24 hours. It is important to flush the toilet and wash your hands thoroughly after each time you urinate.

How It Feels

You may find it uncomfortable to lie still with your head tipped backward.

Risks

There is always a slight chance of damage to cells or tissue from radiation, including the low levels of radiation used for this test. But the chance of damage from the radiation is usually very low compared with the benefits of the test.

This test is not done for pregnant women because of the chance of exposing the baby (fetus) to radiation. This test is also not recommended for breast-feeding women or young children.

Results

A radioactive iodine uptake (RAIU) test uses a radioactive tracer and a special probe to measure how much tracer the thyroid gland absorbs from the blood. The radioactive tracer used in this test is iodine. An RAIU test is done to check for thyroid gland problems, such as hyperthyroidism.

Radioactive thyroid scan and radioactive iodine uptake test (RAIU)
Normal:

The amount of radioactive tracer in the thyroid gland is normal. An RAIU test measures the amount of tracer taken up by the thyroid gland at certain times after the tracer is given. The measured amount of radioactive tracer in the thyroid gland at each one of these times is at normal levels.

Abnormal:

The test shows either more or less uptake of tracer than normal in the thyroid gland. The uptake may be even or uneven. If hyperthyroidism is present, abnormal test results may mean certain conditions are present.

  • A low uptake of tracer by the thyroid gland may mean that hyperthyroidism is caused by inflammation of the thyroid gland (thyroiditis), taking too much thyroid medicine, or another rare condition.
  • A high uptake of tracer spread evenly in the thyroid gland may mean that hyperthyroidism is caused by conditions such as Graves' disease.
  • An uneven spread of tracer in the thyroid gland (with either low or high areas of uptake) may mean that hyperthyroidism is caused by a multinodular goiter or a noncancerous (benign) tumor called a toxic adenoma.

WebMD Medical Reference from Healthwise

Last Updated: May 31, 2011
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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