Thyroid-binding globulin
Thyroid-binding globulin (TBG) is a globular plasma protein whose function is to bind and transport thyroxine and triiodothyronine. Congenital TBG deficiency is asymptomatic, making TGB's physiological importance uncertain.
The level of TBG can be measured if congenital TBG deficiency is suspected, as this will interfere with regular thyroid hormone measurement.