Iodine Uptake And Thyroid Scan

Radioactive iodine uptake, RAIU, and radioiodine thyroid uptake and/or scan.

• To determine the size, structure, and function of the thyroid gland.
• To diagnose the cause of an overactive thyroid gland.
• To evaluate thyroid nodules for activity, inactivity, and malignancy.
• The scan alone may be used to determine the extent of thyroid cancer.

These two tests, which are almost always done together, are based on the fact that iodine is taken up easily by the thyroid gland (which converts it to hormones) but only minutely by other body tissues. By tagging iodine or a similar substance with a radioisotope, it is possible to measure the amount absorbed by the thyroid gland (the uptake study) or, by using a gamma scintillation camera, to actually see the thyroid tissue (the scan).

• Your physician will give you a list of drugs (including thyroid hormones) as well as foods containing iodine (such as shellfish) to avoid during the week before the test.
• Blood samples for thyroid function tests will be drawn before the injection.
• You may have a thyroid ultrasound exam before (or after) the scan.
• If you are to take radioactive iodine in oral form, you will be asked to fast for anywhere from two to 12 hours before the test.
• For day two of the test, wear a loose-fitting T-shirt to make hyperextending your neck as comfortable as possible.

• You will be given a small dose of radioactive iodine, orally or by injection.
• You will return in 6 and/or 24 hours to check the uptake of the iodine.
• A stationary probe (which doesn't generate, but only measures, radioactivity) will be aimed at your neck and the amount of uptake recorded.
• For the scan, a radioisotope is injected into the vein in your arm.
• You will lie on your back on a table while your head is stretched backward and your neck hyperextended. A pillow is placed under your neck to make this more comfortable.
• A gamma scintillation camera detects the radioisotope that collects in your thyroid gland over 20 to 30 minutes, and produces an image on a screen. Photographs can also be taken for further analysis.
• The time needed to produce the pictures depends on how long it takes the isotope to travel to the thyroid. More time may be necessary if special views of the thyroid are taken.

You are free to leave and resume normal activities.

Failure to refrain from using iodine-containing compounds and foods.

The results of the uptake test are expressed as the percentage of the dose taken up by the thyroid gland. A high intake indicates an overactive thyroid gland.

The test effectively assesses the anatomy of and measures the function of the gland.

It entails low-level exposure to a radioactive substance.

The test is considered definitive, and treatment can begin.