RAIU

RAIU stands for Radioactive Iodine Uptake. It is a nuclear medicine procedure used to measure the thyroid’s ability to take up iodine, providing information about thyroid function and activity. The test typically uses a small oral dose of radioactive iodine, most commonly Iodine-123 for diagnostic uptake; Iodine-131 may be used in some planning or therapeutic contexts. After administration, uptake is measured with a gamma camera at specified times, usually around 6 hours and 24 hours. The percentage of the administered dose that localizes in the thyroid is calculated and interpreted.

Normal uptake values vary by laboratory and patient iodine status, but in euthyroid individuals with adequate iodine intake, typical ranges are about 5–15% at 6 hours and 15–30% at 24 hours. Results are interpreted in the context of clinical presentation and, if needed, thyroid imaging.

Indications include evaluation of hyperthyroidism to determine its cause and activity, differentiation of Graves’ disease from thyroiditis or exogenous iodine exposure, and assessment to guide therapeutic decisions, such as radiation therapy planning or surgical considerations. It can also be used in conjunction with thyroid scintigraphy to evaluate nodular disease.

Preparation and safety: patients should avoid iodine-containing medications and contrast agents for an interval before the test, as directed by the clinician. Pregnancy and lactation are contraindications; a pregnancy test is usually performed for women of childbearing potential. The procedure involves a small radiation exposure and is generally well tolerated.

Limitations: recent iodine intake or interfering medications can affect results; interpretation relies on integration with clinical findings and other laboratory data.