What is the role of testing T4 levels in hypothalamic or pituitary dysfunction in the evaluation of hypothyroidism?

Updated: Mar 03, 2021
  • Author: Philip R Orlander, MD, FACP; Chief Editor: George T Griffing, MD  more...
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In patients with hypothalamic or pituitary dysfunction, TSH levels do not increase in appropriate relation to the low free T4 levels. The absolute levels may be in the reference range or even slightly elevated while still being inappropriately low for the severity of the hypothyroid state. Hence, when secondary or tertiary hypothyroidism is suspected, measurement of serum TSH alone is inadequate; free T4 should also be measured.

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