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Thyroid Hormone Binding Globulin

Meaning

Thyroid Hormone Binding Globulin (TBG) is the principal transport protein in the bloodstream responsible for carrying the majority of the circulating thyroid hormones, thyroxine (T4) and triiodothyronine (T3). This glycoprotein, synthesized in the liver, binds to the thyroid hormones with high affinity, effectively rendering them inactive and protecting them from metabolic degradation. TBG plays a crucial role in maintaining a stable reservoir of thyroid hormones, ensuring a constant supply to peripheral tissues despite the pulsatile secretion from the thyroid gland. Clinically, alterations in TBG concentration, often due to changes in estrogen levels or liver function, can significantly impact the interpretation of total T4 and T3 measurements.