radioactive iodine uptake (RAIU), the absorption and incorporation by the thyroid of radioactive iodine (RAI), administered orally as a tracer dose in a test of thyroid function and in larger doses for the treatment of hyperthyroidism. The radioisotope 131I is rapidly absorbed in the stomach and concentrated in the thyroid. Normal findings are 4% to 12% absorbed in 2 hours, 6% to 15% absorbed in 6 hours, and 8% to 30% absorbed in 24 hours. Patients receiving a large therapeutic dose of RAI may require hospitalization for several days. See also radioactive iodine excretion test.
