RAIU is used to differentiate causes of hyperthyroidism. You cannot do a RAIU thyroid scan if the patient recently got IV contrast or an amiodarone load because iodine blocks uptake of radioactive iodine (RAI). In that case, you will check autoantibodies instead. On a personal note, we admitted a patient with thyrotoxic periodic paralysis who received
On a personal note, we admitted a patient with thyrotoxic periodic paralysis who received amiodarone in the ED. Because of that, we couldn’t do the RAIU scan during that hospitalization. The Patient had to f/u with endocrine outpatient to do it weeks down the line.
Increased Uptake
- Homogenous = Graves’ disease (the most common cause).
- Heterogenous = Multinodular goiter = An enlarged thyroid gland that contains nodules producing too much thyroid hormone (toxic nodular goiter)
- Single focus = A single thyroid nodule that is producing too much thyroid hormone (toxic adenoma)
Multinodular goiter and toxic adenoma “often result in a normal uptake, but the uptake is concentrated into a few (hot) areas while the rest of the thyroid gland does not take up any iodine (cold areas). This can only be determined if the scan is done along with the uptake test.”
What is a hot nodule? A hot nodule = One focus of uptake with suppression of the rest of the gland.
No uptake / Lower than Normal Uptake.
Lower-than-normal uptake may be due to:
- Subacute thyroiditis (painful swelling or inflammation of the thyroid gland)
- Silent (or painless) thyroiditis
- Postpartum thyroiditis.
- Exogenous thyroid ingestion / Factitious hyperthyroidism (taking too much thyroid hormone medicine or supplements)
- struma ovarii,
- Iodine overload. Recent iodine load
- Amiodarone
- Antithyroid drugs.