A radioactive iodine uptake (RAIU) test uses a radioactive tracer and a special probe to measure how much tracer the thyroid gland absorbs from the blood. The radioactive tracer used in this test is iodine. An RAIU test is done to check for thyroid gland problems, such as hyperthyroidism.
Normal: The amount of radioactive tracer in the thyroid gland is normal. An RAIU test measures the amount of tracer taken up by the thyroid gland at certain times after the tracer is given. The measured amount of radioactive tracer in the thyroid gland at each one of these times is at normal levels.
Abnormal: The test shows either more or less uptake of tracer than normal in the thyroid gland. The uptake may be even or uneven. If hyperthyroidism is present, abnormal test results may mean certain conditions are present.
- A low uptake of tracer by the thyroid gland may mean that hyperthyroidism is caused by inflammation of the thyroid gland (thyroiditis), taking too much thyroid medicine or another rare condition.
- A high uptake of tracer spread evenly in the thyroid gland may mean that hyperthyroidism is caused by conditions such as Graves' disease.
- An uneven spread of tracer in the thyroid gland (with either low or high areas of uptake) may mean that hyperthyroidism is caused by a multinodular goiter or a noncancerous (benign) tumor called a toxic adenoma.
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