Thyroxine Binding Globulin
What is TBG?
T3 (Triiodothyronine) and T4 (Thyroxine) hormones are produced by the thyroid gland which binds with the proteins produced by the body. However, small amounts of T3 and T4 remains ‘free’ as it does not bind with the proteins. The protein bound T3 and T4 binds to Thyroxine Binding Globulin (TBG). TBG test is done to assess the thyroid tissues. It helps in the diagnosis of other thyroid disorders such as hypothyroidism and hyperthyroidism.This test measures the levels of TBG which helps in assessing thyroid problems.
Why is TBG done?
To diagnose hypothyroidism (low levels of thyroid)
To diagnose hyperthyroidism (high levels of thyroid)
To monitor treatment in patients with thyroid disease
What does TBG Measure?
Thyroxine Binding Globulin (TBG) test measures the levels of TBG which helps in assessing thyroid problems.
TBG is a serum binding protein which has a high affinity to bind to T3 and T4. In the routine, the thyroid gland maintains the level of free hormone i.e. which is not bound to the TBG. This test is done to assess the thyroid tissues. It helps in diagnosing thyroid disorders such as hypothyroidism and hyperthyroidism. The rise in levels is associated with the intake of oral contraceptives or estrogen therapy. Elevated levels of TBG can be seen during pregnancy or if a person has a family history. The decrease in TBG levels is associated with the intake of androgenic steroids, heavy doses of glucocorticoids, liver disease, nephrotic syndrome, congenital TGB variants and hypoproteinemic states
Interpreting TBG results
High levels may indicate:
Acute intermittent porphyria
Low levels may indicate: