Test Detail
Overview
Interpreting Results
FAQ's

Content created by

Written by
Dr. Betina Chandolia
BDS, MDS - Oral Pathology and Microbiology
Reviewed by
Dr. Ashish Ranjan
MBBS, MD (Pharmacology)
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Thyroxine Binding Globulin

(TBG)
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Thyroxine Binding Globulin
You need to provide
Blood
This test is for
Male, Female
Test Preparation
  1. No special preparation required

Overview


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


Interpretations

High levels may indicate:

  • Liver disease

  • Acute intermittent porphyria

  • Hypothyroidism


Low levels may indicate:

  • Acromegaly

  • Acute illness

  • Hyperthyroidism

  • Malnutrition

  • Nephrotic Syndrome

Answers to Patient Concerns & Frequently Asked Questions (FAQs) about TBG


Frequently Asked Questions about Thyroxine Binding Globulin

Q. What is Hypothyroidism?
Hypothyroidism, also called underactive thyroid or low thyroid is a condition in which the thyroid gland does not produce enough thyroid hormones. It can be commonly caused by intake of low iodine diet or Hashimoto's thyroiditis (an autoimmune disease). Less common causes include previous treatment with radioactive iodine, injury to the pituitary gland which secretes TSH, intake of certain medicines, previous thyroid surgery, or a lack of a functioning thyroid gland at birth.
Q. How is this test performed?
This test is performed on a blood sample. A syringe with a fine needle is used to withdraw blood from a blood vessel in your arm. The healthcare provider will tie an elastic band around your arm to make the blood vessels swell with blood. This makes it easier to withdraw blood. You may be asked to tightly clench your fist. Once the veins are clearly visible, the area is cleaned with an antiseptic solution and then the needle is inserted into the blood vessel to collect the sample. You will feel a tiny pinprick during the procedure. Blood sample once collected will then be sent to the laboratory.
Q. Is there any risk associated with this test?
There is no risk associated with the test. However, since this test involves a needle prick to withdraw the blood sample, in very rare cases, a patient may experience increased bleeding, hematoma formation (blood collection under the skin), bruising or infection at the site of needle prick.
Q. What additional tests can be performed in case the TBG results are not in the normal range?
If the TBG test results are not in the normal range, your doctor may ask for the following tests: Thyroid profile Free Anti Thyroperoxidase Antibody
Q. Can medicines have any effect on the levels of TBG test?
Yes, certain medicines such as prednisone, phenothiazines, dilantin, depakene, depakote, drugs such as opioids and opiates or hormonal therapy such as estrogen therapy can affect the levels of TBG.
Q. What is Hyperthyroidism?
Hyperthyroidism is a condition in which the thyroid gland is overactive and there is an increased production of thyroid hormones by the thyroid gland. Causes of Hyperthyroidism include Graves’ disease, multinodular goiter, thyroid nodules, toxic adenoma, inflammation of the thyroid, eating too much iodine, and too much synthetic thyroid hormone. Diagnosis of this condition can help to relieve the symptoms and prevent long-term complications.
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