TBG levels depend on the levels of which substance?

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Multiple Choice

TBG levels depend on the levels of which substance?

Explanation:
Thyroxine-binding globulin (TBG) is made by the liver and acts as the transport protein for thyroid hormones. Its amount in the blood is mainly determined by hepatic synthesis, which is strongly increased by estrogen. That’s why TBG levels rise in pregnancy or with estrogen therapy, causing higher total T4 and T3 without changing the free (active) hormone levels. TBG is not directly controlled by the actual levels of T4, TSH, or rT3. So, in normal physiology, estrogen is the key regulator of TBG concentration. If a key lists thyroglobulin as the determinant, that reflects a miskey; the correct regulator is estrogen.

Thyroxine-binding globulin (TBG) is made by the liver and acts as the transport protein for thyroid hormones. Its amount in the blood is mainly determined by hepatic synthesis, which is strongly increased by estrogen. That’s why TBG levels rise in pregnancy or with estrogen therapy, causing higher total T4 and T3 without changing the free (active) hormone levels. TBG is not directly controlled by the actual levels of T4, TSH, or rT3. So, in normal physiology, estrogen is the key regulator of TBG concentration. If a key lists thyroglobulin as the determinant, that reflects a miskey; the correct regulator is estrogen.

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