THBR stands for which term?

• A. Thyroid Hormone Binding Ratio
• B. Thyroid Hormone Binding Receptor
• C. Thyroxine Hormone Binding Ratio
• D. Therapeutic Hormone Binding Ratio

Answer: (A)

Thyroid hormones in the blood are mostly bound to transport proteins, and only the free hormone can act on tissues. THBR stands for Thyroid Hormone Binding Ratio, which describes the balance between the bound and the free hormone in circulation. This ratio matters because changes in binding proteins (like during pregnancy, with estrogen therapy, or liver disease) can alter total thyroid hormone levels without changing the active free hormone. So, the term correctly captures the concept of how much hormone is carried by binding proteins versus how much is available to exert biological effects.

The other options don’t fit the intended meaning: one would imply a cellular receptor, which is not what this ratio describes; another specifies only thyroxine, whereas THBR refers to thyroid hormones in general; and a therapeutic term isn’t relevant to standard thyroid binding assessments.