Normal Radioactive Iodine Uptake (RAIU) Range

B. 10–35%

In the United States, the normal 24-hour RAIU is approximately 10–35% (the exact range varies by laboratory but typically 15–35%). This range is lower than in iodine-deficient countries because Americans consume a relatively iodine-sufficient diet (from iodized salt, seafood, dairy), which dilutes the administered radioiodine with stable iodine and reduces fractional uptake. RAIU >35% at 24 hours suggests hyperthyroidism (Graves', toxic MNG, toxic adenoma). RAIU <10% suggests hypothyroidism, thyroiditis, iodine excess, or recent iodine load. RAIU measurement requires accurate background correction and proper probe calibration.