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.