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The thyroid is a small gland in the lower front of the neck. It produces thyroid hormone, which helps control the body’s metabolism. A thyroid uptake measures how well the thyroid gland is working. A thyroid scan shows the size, shape, and location of the thyroid gland. The tests are usually done together to check for problems in the thyroid gland. This sheet tells you what to expect with each test.
Prepare for the test as you’ve been told. In addition:
Be sure your doctor knows about all medicines you take because you may need to stop taking some or all of them before the test. This includes:
Over-the-counter medicines that don't need a prescription
Any street drugs you may use
Any iodine or thyroid medications
Herbs, vitamins, kelp, seaweed, cough syrups, and other supplements
Follow any directions you’re given for not eating or drinking before the test.
For your safety, tell the technologist if you:
Are pregnant or might be pregnant.
Are taking any medications.
Are allergic to iodine, anesthetics, or any medications.
Had a recent nuclear medicine scan or other tests that used iodine.
Have other health problems, such as diabetes or kidney problems.
Have any allergies
Have any current medical illnesses or long-time medical conditions
The test is performed by a nuclear medicine technologist or doctor. The length of the test varies depending on the method(s) used to perform each procedure and whether you’re having only one or both tests done.
Before the test:
For the thyroid uptake test: You’ll be asked to swallow a capsule or drink a liquid that contains radioactive iodine. You will have to wait 4 or more hours before having the uptake test to give the iodine time to collect in your thyroid.
For the thyroid scan: You'll be asked to swallow a capsule or drink a liquid that contains radioactive iodine in most cases. But a technetium (also known as Technetium-99m) tracer can be used and injected in the vein. If the technetium tracer is used, it is put through an intravenous (IV) line into a vein in your hand or arm. You may only need to wait about 30 minutes before having the scan done.
During the test:
For the thyroid uptake test, you’ll need to sit upright. A small device is then placed at the front of your neck. The device measures the amount of iodine that has collected in your thyroid.
For the thyroid scan, you’ll lie down on a narrow table. A special camera (called a gamma camera) is then positioned over your neck. Pictures of your thyroid are taken from different angles. You’ll need to lie still during this process. The camera detects the location and areas where the radioactive iodine or technetium tracer has collected in your thyroid.
After the test:
You may need to return in 24 hours to have a second uptake, scan, or both done.
Unless told not to, you can return to your normal routine shortly after the test. The radioactive iodine will pass out of your body in your urine within days after the exam.
Rash or hives
Nausea or vomiting
The nuclear medicine doctor will review the results of your tests and send a report to your doctor. Your doctor will then discuss the results with you when they are ready. This will likely be within a week after the test.
A thyroid scan and uptake can pose certain risks if you are pregnant or breastfeeding. Be sure to talk to your doctor about these risks before you have either test.