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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. For both tests, a small amount of radioactive iodine is used. If you’re allergic to iodine, a substance called technetium may be used instead. This sheet tells you what to expect with each test.
Prepare for the test as you’ve been told. In addition:
Tell the doctor if you take any medications. Be sure to mention if you take any iodine or thyroid medications. Also, mention if you take over-the-counter drugs, herbs, and other supplements. You may need to stop taking some or all of them before the test.
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 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.
The test is performed by a nuclear medicine technologist or doctor. The length of the test varies depending on the method used to give the radioactive iodine and whether you’re having only one or both tests done.
Before the test:
You’ll be asked to swallow a pill or drink a liquid that contains radioactive iodine. You may then wait at the facility or leave and return in about 4-6 hours before having the uptake, scan, or both done. This gives the iodine time to collect in your thyroid.
In some cases, the radioactive iodine may be given by IV. With this method, an IV line is put into a vein in your hand or arm. The iodine is then injected through the IV. You may only need to wait about 30 minutes before having the uptake and scan done.
During the test:
For the 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 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 iodine 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 24 hours.
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.