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 absorbs from the blood. The test can show how much tracer is absorbed by the thyroid gland and if it 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. An RAIU test may be done at the same time as a thyroid scan.
Why It Is Done
A radioactive iodine uptake (RAIU) test is done to:
How To Prepare
Tell your doctor if you:
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:
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.
Before a radioactive iodine uptake (RAIU) test, you need 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?).
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.
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.
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.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
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