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Thyroxine Binding Globulin, Serum

Thyroxine Binding Globulin, Serum

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The Thyroxine Binding Globulin, Serum test is a blood test that measures the level of thyroxine binding globulin (TBG), a protein that binds thyroid hormones. It helps interpret thyroid hormone tests  when total T3/T4 levels are discordant with clinical findings.

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Understanding Thyroxine Binding Globulin, Serum

Thyroxine binding globulin (TBG) is a protein produced by the liver that carries thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), in the blood. Only a small fraction of thyroid hormones circulates freely, while most are bound to proteins like TBG. The Thyroxine Binding Globulin, Serum test measures how much of this protein is present in the blood, which affects interpretation of total thyroid hormone levels and helps assess hormone transport.

Doctors may recommend this test when there are general symptoms suggestive of thyroid imbalance such as constipation, dry skin, diarrhea, puffy skin, tiredness, hair loss, weakness, sensitivity to cold or heat, fast heartbeat, weight changes, or irregular periods, particularly when thyroid hormone results (total T3/T4) appear unusual or unclear relative to free hormone levels or clinical picture. This test is advised for conditions affecting hormone-binding proteins, such as pregnancy, liver disease, nephrotic syndrome, or suspected genetic TBG disorders.

No special preparation is required for the Thyroxine Binding Globulin, Serum test. Inform the doctor about all the medications and supplements currently being taken, as these may affect the test results.

Test result ranges are approximate and may differ slightly between labs depending on the methodology and laboratory guidelines. Do not self- diagnose and always consult a doctor to understand the test results correctly. 

Please note: This is an outsourced test. The sample for this test is collected by TATA 1MG and processed at a NABL accredited partnered lab.

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What does Thyroxine Binding Globulin, Serum measure?

The Thyroxine Binding Globulin, Serum test measures the level of thyroxine-binding globulin, the protein that binds thyroid hormones in the blood. By controlling how much hormone is bound and free, TBG regulates the amount of active thyroid hormone available to tissues.

High TBG levels may be seen in pregnancy, estrogen therapy, or certain liver diseases, whereas low TBG levels may occur in protein deficiency, severe illness, or androgen therapy. Abnormal TBG levels can alter total T4 and T3 measurements, so the Thyroxine Binding Globulin, Serum test helps doctors interpret thyroid hormone tests more accurately and support clinical decision-making.

FAQs related to Thyroxine Binding Globulin, Serum

The Thyroxine Binding Globulin, Serum test measures the level of thyroxine-binding globulin, a protein that carries thyroid hormones (T3 and T4) in your blood. It helps doctors understand how thyroid hormones are transported and how much is available to your body.
Thyroid hormones are mostly bound to proteins like TBG. Abnormal TBG levels can affect total thyroid hormone levels, so this test helps doctors interpret thyroid function tests accurately.
Your doctor may recommend it: If your total T3 or T4 levels are abnormal; To check thyroid function during pregnancy or hormone therapy; If there is suspected liver or kidney disease; To evaluate suspected genetic TBG deficiencies or excesses.
No, fasting is not required for the TBG test. You can eat and drink as usual unless your doctor tells you otherwise.
It is just a simple blood test with minimal risk (minor needle discomfort/bruising). You might feel a small pinch when the needle is inserted, but it is quick and usually not very painful.
High TBG levels can occur in pregnancy, estrogen therapy, or some liver conditions. Low TBG levels may occur in protein deficiency, severe illness, or androgen therapy. Doctors use these results along with other thyroid tests to understand your overall thyroid health.
TBG (thyroxine-binding globulin) is a protein made by the liver that carries thyroid hormones (T3 and T4) in the blood.
TBG helps transport thyroid hormones to different parts of the body. While most hormones are bound to TBG, only a small amount remains “free” and active. This free portion is what controls metabolism, energy, and body functions.
Not always. Abnormal TBG levels may simply affect how thyroid hormones appear in blood tests. For example, if TBG is high, total hormone levels may look high even if the thyroid is normal. If TBG is low, hormone levels may look low. That is why doctors use TBG testing along with other thyroid tests for accurate results.
High TBG levels can happen in pregnancy, during estrogen therapy, or in some liver conditions.
Low TBG levels may occur in severe illness, genetic conditions, protein deficiency, or with androgen (male hormone) therapy.
This is because changes in TBG can make thyroid hormone results misleading. Testing TBG helps doctors understand the real thyroid status and decide if symptoms are due to the thyroid itself or just changes in hormone-binding proteins.
Tata 1mg ensures accurate lab test results through certified laboratories that use advanced technology and adhere to stringent quality control measures. This commitment to high standards guarantees reliable results.
Content created by
Written by:
Dr. Lipika Khurana
BDS, PGDHHM
Reviewed by:
Dr. Swati Gupta (Anand)
MD Lab Medicine, MBBS
Want to know moreRead our editorial policy
Last Updated10th Feb 2026

Thyroxine Binding Globulin, Serum test price for other cities

Price inBangaloreRs. 6159
Price inAligarhRs. 6159
Price inBardhamanRs. 6159
Price inAsansolRs. 6159
Price inChandigarhRs. 6159

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Thyroxine Binding Globulin, Serum