Thyroid-binding globulin (TBG) is produced in the liver and is the primary circulating (transport) protein that binds thyroid hormones3,5,3’-triiodothyronine (T3) and thyroxine (T4) and carries them in the bloodstream (think of it like a taxi cab that shuttles T3 and T4 around the body).
There are 2 other thyroid hormone transport proteins (Transthyretin & serum Albumin), but TBG has the highest affinity (=the degree to which a substance tends to combine with another) for T4 and T3 but is present in the lowest concentration.
Decreased TBG levels may be due to:
An increased TBG level may be due to:
Note: TBG levels are normally high in newborns.
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