Radioactive Iodine Uptake Test
How It Feels
You may find it uncomfortable to lie
still with your head tipped backward.
There is 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
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
Radioactive thyroid scan and radioactive iodine uptake test (RAIU)
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.
The test shows either more or less uptake
of tracer than normal in the thyroid gland. 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
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
- Taking thyroid medicine.
foods with iodine, such as shellfish, iodized salt, or kelp.
- Having other tests using
contrast materials in the past 4 weeks.
What To Think About
- Blood tests may be done before a radioactive
iodine uptake (RAIU) to measure the amount of thyroid hormones (TSH, T3, and
T4) in your blood.
- A thyroid scan may
be done at the same time as an RAIU test. To learn more, see the topic