A combination of elevated TSH, T3 and T4 levels is seen in TSH-secreting pituitary adenoma or thyroid hormone resistance syndrome. These disorders can be differentiated by measuring
A) Thyroid binding gobulin
B) Anti TPO
C) Alpha-subunit levels in the serum.
D) TRH
E) Prolactin
C
Assay of the TSH alpha subunit is indicated where thyrotoxicosis appears to be the result of central autonomous TSH excess to distinguish this entity from thyroid hormone resistance. Most TSH producing pituitary adenomas show an increase in alpha subunit, whereas levels generally remain normal in thyroid hormone resistance