Thyroid binding or Thyroid Binding Globulin helps in binding together the thyroid hormones that circulate in the human body. It is a protein, which along with albumin and transthytretin, help in carrying thyroxine (T4), which is a thyroid hormone. It is produced in the liver of a human being and it is primarily responsible for the transportation of the thyroid hormones T4 and T3 from the thyroid gland to the blood stream, so that they can mix with the blood and then spread to the other organs of the body. It is secreted in a very minimum amount and the deficiency of this hormone can cause many diseases.
What does it do?
The thyroxine-binding globulin (TBG) is a glycoprotein whose molecular mass is 1800 kDa , binds to the blood circulation to the thyroid hormones T4 and T3 with an affinity 100 times greater than that of thyroxine-binding prealbumin (TBPA) . In normal conditions TBG non-covalently fixes almost the entire concentration of T3 and T4. The portion of the thyroid hormone that is not fixed is in charge of producing biological activity.
The TBG is produced in the liver and its synthesis is increased by the action of estrogen .Its synthesis decreases after treatment with androgens or glucocorticoids and in some liver diseases, which are inherited. In such diseases the liver fails to produce the required amount of Thyroid Binding Globulin.
What is its importance?
It has a major role to play in the diagnosis of many thyroid related problems in the body. The Thyroid Binding Globulin or TGB level in the body is measured to determine the root cause of thyroid diseases like hypothyroidism, hyperthyroidism etc. Testing TGB levels can help in determining the reasons for decrease or increase in thyroid hormones, which in turn helps in the treatment of many thyroid diseases.