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.
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:
- Find the cause of an overactive thyroid gland
- Plan treatment for hyperthyroidism.
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 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 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:
- Do not eat for 2 hours before the
- Do not take any antithyroid medicine for 5 to 7 days before
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
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
medical test information form(What is a PDF document?).