*5.3.2 Radioiodine uptake (RAIU) and thyroid scan*

RAIU measures the percentage of administered RAI that is concentrated into thyroid tissue after a fixed interval, usually 24 hours. Technetium uptake measurements utilize pertechnetate that is trapped by the thyroid, but not organified. A technetium (TcO4) uptake measures the percentage of administered technetium that is trapped by the thyroid after a fixed interval, usually 20 minutes. Uptake study is not indicated routinely. It is recommended only when diagnosis is difficult. Uptake is increased in GD, toxic multinodular goiter and toxic adenoma. Uptake is decreased in subacute, postpartum, painless thyroiditis.
