Thyroxine-Binding Globulin (TBG) Test
Clarify how your thyroid hormones are transported and bound.
The Thyroxine-Binding Globulin (TBG) test measures the level of TBG, a liver-produced protein that binds and transports the majority of thyroxine (T4) and triiodothyronine (T3) in the bloodstream. This test is typically requested when thyroid function tests show unexpected results, such as abnormal total T4 or T3 levels that do not match the patient's clinical picture. It helps clinicians determine whether altered thyroid hormone levels are due to changes in binding proteins rather than actual thyroid dysfunction. It is also used to investigate suspected inherited or acquired TBG abnormalities, and to monitor conditions or medications that can affect TBG concentrations.
Biomarkers included
- Thyroxine-Binding Globulin (TBG)
Why it matters
TBG plays a central role in regulating the amount of free, active thyroid hormone available to tissues. Measuring TBG helps distinguish true thyroid disorders from harmless shifts in binding protein levels, guiding accurate diagnosis and avoiding unnecessary treatment. This is particularly valuable in situations where total thyroid hormone results are misleading, such as during pregnancy, in liver disease, or when certain medications are used.
- Thyroxine-Binding Globulin (TBG)
No special preparation required.
For blood tests, we recommend drinking plenty of water beforehand to ensure smooth sample collection. If you are taking any regular medication, continue to do so unless advised otherwise by your doctor.
Important Clinical Information:
This test is a screening tool to monitor and support your overall health. It does not replace your GP or consultant.
Always discuss your test results, especially any abnormal results, with your GP, who can interpret them in the context of your medical history and overall health.