Which test measures the thyroid gland's uptake of radioactive iodine and helps differentiate causes of hyperthyroidism?

Which test measures the thyroid gland's uptake of radioactive iodine and helps differentiate causes of hyperthyroidism?

• A. FNA biopsy
• B. TSH receptor antibodies
• C. RAIU
• D. TSH

Answer: (C)

Measuring how much radioactive iodine the thyroid takes up is a functional test that helps differentiate causes of hyperthyroidism. In this test, a small amount of radioactive iodine is given and the thyroid’s uptake is measured after a short interval. The pattern of uptake tells you how the gland is functioning. Graves disease usually shows diffuse, high uptake because the entire gland is overactive. Toxic multinodular goiter or a toxic adenoma tends to have high uptake as well, but it’s uneven or focal, reflecting autonomous areas of hormone production. Thyroiditis or a release of preformed hormone, on the other hand, produces low uptake since the gland isn’t actively synthesizing new hormone. So this test not only confirms hyperthyroidism but also suggests the likely cause based on the uptake pattern. Other available tests either assess autoimmune antibodies, measure pituitary signals, or sample tissue, but they don’t provide the same information about iodine uptake and its distribution.

Measuring how much radioactive iodine the thyroid takes up is a functional test that helps differentiate causes of hyperthyroidism. In this test, a small amount of radioactive iodine is given and the thyroid’s uptake is measured after a short interval. The pattern of uptake tells you how the gland is functioning. Graves disease usually shows diffuse, high uptake because the entire gland is overactive. Toxic multinodular goiter or a toxic adenoma tends to have high uptake as well, but it’s uneven or focal, reflecting autonomous areas of hormone production. Thyroiditis or a release of preformed hormone, on the other hand, produces low uptake since the gland isn’t actively synthesizing new hormone. So this test not only confirms hyperthyroidism but also suggests the likely cause based on the uptake pattern. Other available tests either assess autoimmune antibodies, measure pituitary signals, or sample tissue, but they don’t provide the same information about iodine uptake and its distribution.