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Alternative names Return to top
Iodine uptake test; RAIUDefinition Return to top
Radioactive Iodine Uptake, or RAIU, is a test of thyroid function. The amount of orally ingested radioactive iodine that accumulates in the thyroid gland (see also "thyroid scan") is measured.How the test is performed Return to top
RAIU is a type of nuclear test of the thyroid that measures how much radioactive iodine is taken up by the thyroid gland in a given time period. You are asked to ingest radioactive iodine (I-123 or I-131) in liquid or capsule form. After a time (usually 6 and 24-hours later), you must return to have the radioactivity measured.
A probe (gamma probe) is placed over the thyroid gland in the neck to measure the amount of radioactivity in the thyroid gland. This amount of radioactivity is compared with the original dose of radioactivity and reported as a percent of the original dose.
How to prepare for the test Return to top
Fast for 8 hours before the test.How the test will feel Return to top
There is no discomfort. You can eat beginning about 1 to 2 hours after ingesting the radioactive iodine, and you can resume a normal diet when the test is finished. For the scanning, you are asked to lie on a table while the scanner is placed over the neck. The scan takes about 30 minutes.Why the test is performed Return to top
This test is performed to evaluate thyroid function, particularly when blood tests of thyroid function (for example, T3 or T4 levels) have abnormal results.Normal Values Return to top
What abnormal results mean Return to top
Increased (greater than 35% at 24-hours is considered elevated): Decreased:What the risks are Return to top
The risk is minimal. The amount of radioactivity is very small and there have been no documented side effects. However, as with any radiation exposure, this test is not recommended for women who are pregnant or breastfeeding.Special considerations Return to top
The radioactive iodine is excreted in the urine. However, the amount of radioactivity is minute, so special precautions may or may not be advised for 24 to 48 hours (often this simply includes flushing twice after urinating). Consult the health care provider or the radiology/nuclear medicine department performing the scan.
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Page last updated: 28 October 2004 |