Thyroid testing

Published on 02/03/2015 by admin

Filed under Endocrinology, Diabetes and Metabolism

Last modified 02/03/2015

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CHAPTER 32

Thyroid testing

1. What is the single best test to screen for abnormal thyroid gland function?

2. How do you interpret the serum TSH level?

3. Explain how the serum TSH is used to manage patients undergoing thyroid hormone therapy.

4. Discuss the advantages of free thyroid hormone assays.

5. What do total T4 and T3 assays measure?

6. Name the major disorders of thyroid hormone-binding proteins.

Pregnancy, estrogen use, congenital TBG excess, and familial dysalbuminemic hyperthyroxinemia (FDH) are the most common. FDH is an inherited disorder in which albumin has enhanced affinity for T4, resulting in increased levels of total T4 but not T3. Protein binding of T4 and T3 is reduced by androgens and congenital TBG deficiency.

A T3 resin uptake (T3RU) measurement helps distinguish protein-binding disorders from true thyroid diseases. The T3RU is inversely proportional to the protein-binding capacity; accordingly, T3RU is low when T4 protein binding is increased and high when T4 protein binding is reduced. Table 32-1 indicates how these tests are used to make the correct diagnosis.

TABLE 32-1.

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