Individual test · Labcorp 001735

Thyroxine-binding Globulin (TBG), Serum

This test measures the level of thyroxine-binding globulin (TBG), a protein in your blood that transports thyroid hormones. It helps clarify whether abnormal thyroid test results are caused by a problem with the thyroid gland itself or simply a change in the proteins that carry the hormones. This distinction helps doctors rule out conditions like hyperthyroidism when high hormone levels are actually due to pregnancy, medication, or genetics. However, this test does not measure the active thyroid hormones available for your body to use and cannot diagnose thyroid disease without other thyroid function tests.