A radioactive iodine uptake test is a procedure used in the diagnosis of diseases of the thyroid gland. The patient is given low doses of radioactive iodine which is traced over time by the use of a radiological detector known as a scintillation counter.
In a normal patient, 15-25% of the radioactive iodine will be absorbed by the thyroid. Low uptake points to thyroiditis and high uptake points to Graves' disease. If the uptake is uneven, that usually indicates a nodule.
Patients who have recently eaten foods high in iodine content like milk or seafood may have unusual results. In addition, because of the radioactivity, the test should not be given to pregnant or breastfeeding women.