The test involves administering a small amount of radioactive iodine, usually iodine-123 or iodine-131, orally or intravenously. The thyroid gland, which requires iodine for the production of thyroid hormones, absorbs the radioactive iodine. The uptake is then measured using a gamma probe, which quantifies the amount of radioiodine absorbed by the thyroid over a certain period, usually 24 hours.
