Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1238 page)

   Concordance values of T
₄
and THBR tests suggest altered thyroid function.

   Discordant variance suggests primary change in TBG in a euthyroid state (e.g., pregnancy)

THYROID RADIOACTIVE IODINE UPTAKE (RAIU)

   Definition

   A tracer dose of radioactive iodine (
¹³¹
I or
¹²³
I) is administered orally, and the radioactivity over the thyroid is measured at specific time intervals.

   
Normal range:
10–35% in 24 hours depending on local variations in iodine intake.

   Use

   Evaluation of hyperthyroidism associated with low RAIU (e.g., factitious hyperthyroidism, subacute thyroiditis, struma ovarii)

   Distinguish Graves disease from toxic nodular goiter

   Assess function of nodules (“hot” or “cold”)

   Determine location and size of functioning thyroid tissue

   Detect metastases from differentiated thyroid cancers

   Evaluate use of radioiodine therapy

   Determine the presence of an organification defect in thyroid hormone production