The radioactive iodine uptake test, or RAIU test, is a type of scan used in the diagnosis of thyroid problems, particularly hyperthyroidism.he normal uptake is between 15 and 25 percent, but this may be forced down if, in the meantime, the patient has eaten foods high in iodine, such as dairy products and seafood. Low uptake suggests thyroiditis, high uptake suggests Graves' disease, and unevenness in uptake suggests the presence of a nodule.