What is the relationship between Thyroid Hormone Binding Ratio and Thyroxine-Binding Globulin?

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Multiple Choice

What is the relationship between Thyroid Hormone Binding Ratio and Thyroxine-Binding Globulin?

Explanation:
Thyroxine-binding globulin controls how much thyroid hormone is carried in the bound form versus the free, active form. If the Thyroid Hormone Binding Ratio is defined as the ratio of free T4 to total T4, then increasing TBG binds more T4, raising total T4 while the free fraction stays limited by physiology. This lowers the Free/T4 ratio, so the binding ratio moves in the opposite direction to TBG—an inverse relationship. Clinically, conditions that raise TBG (like estrogenic states or some liver diseases) tend to increase total T4 but keep free T4 normal, reducing the THBR. Conversely, when TBG is low, THBR tends to rise.

Thyroxine-binding globulin controls how much thyroid hormone is carried in the bound form versus the free, active form. If the Thyroid Hormone Binding Ratio is defined as the ratio of free T4 to total T4, then increasing TBG binds more T4, raising total T4 while the free fraction stays limited by physiology. This lowers the Free/T4 ratio, so the binding ratio moves in the opposite direction to TBG—an inverse relationship. Clinically, conditions that raise TBG (like estrogenic states or some liver diseases) tend to increase total T4 but keep free T4 normal, reducing the THBR. Conversely, when TBG is low, THBR tends to rise.

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