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. 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.
radioactive iodine uptake test is done to find problems with how the thyroid
gland works, such as
Why It Is Done
A radioactive iodine uptake (RAIU) test
is done to:
- Find the cause of an overactive thyroid gland
- 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:
- Medicines or supplements that contain iodine, such as iodized salt,
kelp, cough syrups, multivitamins, or the heart medicine amiodarone (such as Cordarone or
- 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
- 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
- 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
- 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
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
medical test information form(What is a PDF document?).