What is a thyroid uptake test?

The radioactive iodine uptake test indicates if the thyroid gland is overactive, which is a condition known as hyperthyroidism, states WebMD. The test may help a doctor determine the cause of hyperthyroidism. It is also used when planning treatment for patients after thyroid surgery.

The radioactive iodine uptake test uses radioactive iodine as a tracer in the blood, reports WebMD. A special probe measures how much tracer the thyroid gland absorbs, and a thyroid scan checks how evenly the tracer is spread throughout the gland. Low uptake of the iodine indicates that the cause of the hyperthyroidism may be inflammation; high uptake and an even spread may indicate a condition such as Graves' disease.