Thyroid Binding Globulin Can Put You in a Bind

Thyroid binding globulin (TBG) is a protein that carries thyroid hormone through the blood and keep levels stabilized. Measuring TBG along with T3 and T4 can help determine if changes in thyroid hormones are due to an increase or decreased production, or due to a change in levels of TBG. 

If TBG increases, then total T3 and T4 levels appear increased as well, and if TBC decreases, then T3 and T4 appear decreased. Although TBG can increase in hypothyroidism and decrease in hyperthyroidism, a full thyroid panel is recommended to truly distinguish thyroid dysfunction from alterations in binding proteins. 

Decreased TBG can be seen with hyperthyroidism, malnutrition, hypoproteinemia, kidney dysfunction, major stress, and certain medications.

Increased TBG can be associated with hypothyroidism, pregnancy, oral contraceptives, estrogen-producing tumors, phthalate exposure, and certain medications.

Want to Learn More?

CLICK HERE to learn more about TBG, optimal ranges, thyroid function, etc.