endocrine and metabolic disorders
Overview of Thyroid Function
Radioactive Iodine Uptake and Imaging
Radioactive iodine uptake can be measured. A trace amount of radioiodine is given orally or intravenously; a scanner then detects the amount of radioiodine taken up by the thyroid. The preferred radioiodine isotope is iodine-123, which exposes the patient to minimal radiation (much less than iodine-131). Thyroid iodine-123 uptake varies widely with iodine ingestion and is low in patients exposed to excess iodine. The test is valuable in the Diagnosis (high uptake in Graves disease, low uptake in thyroiditis). It may also help in the calculation of the dose of iodine-131 needed for treatment of hyperthyroidism. Imaging using a scintillation camera can be done after radioisotope administration (radioiodine or technetium 99m pertechnetate) to produce a graphic representation of isotope uptake. Focal areas of increased (hot) or decreased (cold) uptake help distinguish areas of possible cancer (thyroid cancers exist in<1% of hot nodules compared with 10 to 20% of cold nodules). 