What is the normal RAIU uptake at 24 hours?

• A. 0-5%
• B. 5-30%
• C. 30-60%
• D. 60-90%

Answer: (B)

Radioactive iodine uptake at 24 hours shows how much of the administered iodine the thyroid concentrates, reflecting normal thyroid activity. In adults with normal thyroid function, the 24-hour uptake is a modest fraction, typically about 5% to 30% of the administered dose (some labs use 8–25%, but 5–30% is a common reference). Values below this range can occur with factors that reduce uptake (like recent iodine exposure or hypothyroidism), while values well above this range indicate increased thyroid activity such as in hyperthyroidism. Therefore, the range around 5–30% best represents normal 24-hour RAIU uptake. The other ranges describe abnormal, higher uptake or very low uptake not considered normal.