A thyroid scan uses a
radioactive tracer and a special camera to measure how much tracer the thyroid gland absorbs
from the blood. The tracer can be swallowed or can be injected into a vein. It travels through your body, giving off radiation signals. The camera "sees" the signals and can measure how much tracer the thyroid absorbs from the blood.
A thyroid scan can show the size, shape, and location of
the thyroid gland . It can also find areas of the thyroid gland that are
overactive or underactive. The camera takes pictures of the thyroid gland from
three different angles. The radioactive tracer used in this test is either
iodine or technetium.
iodine uptake (RAIU) test may also be done to find problems with how the
thyroid gland works, such as
hyperthyroidism. To learn more, see the topic
Radioactive Iodine Uptake Test.
Another type of thyroid scan, a whole-body
thyroid scan, may be done for people who have had thyroid cancer that has been
treated. The whole-body scan can check to see if cancer has spread to other
areas of the body.
Why It Is Done
A thyroid scan is done to:
- Find the cause of an overactive thyroid gland (hyperthyroidism).
- See whether
thyroid cancer has spread outside the thyroid gland. A
whole-body scan will usually be done for this evaluation.
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 thyroid scan test results:
- Medicines that have 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 with contrast) 4 weeks before the thyroid scan. These
other tests may change the results of the thyroid scan.
- Are or
might be pregnant.
- Are breast-feeding.
Before a thyroid scan, blood tests are usually done to measure
the amount of thyroid hormones (TSH, T3, and T4) in your blood.
To prepare for a thyroid scan:
- Do not eat for 2 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.