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Understanding the Test
Test Measures
Interpreting Results
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Thyroxine - Free

Also known as Free T4
200380 47% Off
You need to provide
This test is for
Male, Female
Test Preparation
  1. No special preparation is required.
  2. It is advisable to stop multivitamins or dietary supplements containing biotin (vitamin B7) for at least 2 days before the test.

Understanding Thyroxine - Free

What is Thyroxine - Free?

A Thyroxine - Free test measures the amount of free form of thyroxine hormone in the blood. This test helps evaluate the functioning of the thyroid gland and detect possible thyroid disorders. It is also performed in combination with free T3 and TSH tests as part of a thyroid profile free test.

Thyroxine or T4 is a thyroid hormone that regulates your body’s metabolism, temperature, blood pressure, heart rate, etc. It is produced along with the T3 hormone and plays an important role in the growth and development of the nervous system and the brain. T4 hormone exists in the blood in two forms: bound (attached to proteins) and free (not attached to proteins). Deranged levels of this hormone can result in either hyperthyroidism (the thyroid gland produces too much T4) or hypothyroidism (the thyroid gland produces less T4). 

A Thyroxine - Free test measures the amount of free thyroxine hormone (T4), which is not attached to any protein. Your doctor may suggest this test if you show symptoms suggestive of hyperthyroidism, like increased appetite, weight loss, sweating, anxiety, tremors, etc., or hypothyroidism, like fatigue, weight gain, dry skin, constipation, etc.

No special preparations are needed for this test. Usually, you do not need to stop taking your thyroid medication before taking this test. However, do let your doctor know about all the medications you take as some of them can affect your thyroid test results. Biotin (Vitamin B7) is a commonly taken over-the-counter supplement that can lead to some aberrancy in your thyroid function tests even when the values are actually normal. Hence, avoid taking biotin 2 days before this test.

Test result ranges are approximate and may differ slightly between different labs depending on the methodology and laboratory guidelines. Talk to your doctor about your specific results. The test results will help them determine your medical condition, make recommendations for lifestyle modifications such as diet and exercise, evaluate whether or not medication will be required to manage your condition, and formulate an overall treatment plan.

What is Thyroxine - Free used for?

A Thyroxine - Free is done:

  • To measure the levels of free T4 hormone in the body.

  • As part of a thyroid profile test along with FT3 and TSH tests.

  • To evaluate symptoms suggestive of an imbalance in thyroid hormone levels, such as fatigue, weight loss, hair loss, and changes to heart rate.

  • To diagnose and monitor the treatment of hypothyroidism or hyperthyroidism.

  • To detect an underactive thyroid gland in newborn babies.

  • To evaluate other disorders, such as thyroid nodules, goiters, and pituitary or hypothalamus gland disorders.

What does Thyroxine - Free measure?

A Thyroxine - Free test measures the free form of thyroxine (T4) hormone made by the thyroid gland. T4 hormone exists in the blood in two forms: bound (attached to proteins) and free (not attached to proteins). Most of the T4 hormone circulating in the blood is bound to proteins and only a small part is free. A delicate balance of bound and free T4 should be maintained to ensure the proper functioning of the body.

Interpreting Thyroxine - Free results




FT4 (pmol/L)


11.0 - 32.0

6 days to 3 months

11.5 - 28.3

4 to 12 months

11.9 - 25.6

1 to 6 years

12.3 - 22.8

7 to 11 years

12.5 - 21.5

12 to 20 years

12.6 - 21.0


12.0 - 22.0

High values than normal reference range are seen in hyperthyroidism and patients with acute thyroiditis.

Low values than normal reference range are seen in hypothyroidism, myxedema, cretinism, chronic thyroiditis, and occasionally, subacute thyroiditis.


Answers to Patient Concerns & Frequently Asked Questions (FAQs) about Thyroxine - Free

Frequently Asked Questions about Thyroxine - Free

Q. Why is a Thyroxine - Free test done?

A Thyroxine - Free test is done to evaluate symptoms of hypothyroidism (weight gain, fatigue, dry skin, hair thinning, slow heart rate, or depression) and hyperthyroidism (weight loss, muscle weakness, anxiety, trouble sleeping, tremors, or frequent bowel movement).

Q. Can I take a Thyroxine - Free test during pregnancy?

Yes, you can take a free T4 test during pregnancy. This test along with others is usually recommended during pregnancy to measure the levels of thyroid hormones, as thyroid disorders can complicate pregnancy.

Q. What do high T4 levels signify?

High T4 levels can lead to a condition called hyperthyroidism in which the thyroid gland produces too much thyroid hormone. Some of the common causes of hyperthyroidism include nodular goiter and thyroiditis.

Q. What happens when the T4 level is low?

Low T4 levels can lead to a condition called hypothyroidism. Some of the common symptoms of hypothyroidism are fatigue and weakness, weight gain, cold intolerance, and constipation.

Q. How can I reduce my T4 levels naturally?

Always consult your doctor if your test results show high levels of T4 hormone. However, some home remedies, including apple cider vinegar, ginger, vitamin B (fish, legumes, milk, and nuts), vitamin D, dairy products, regular exercise, etc., might help you to lower your T4 levels naturally.

Q. Is fasting required for a Free T4 test?

No, fasting is not needed before taking this test. However, your doctor will guide you if any special preparation is required.

Q. What factors can affect the test results of a Free T4 test?

Certain medications like phenobarbital, amiodarone, or diclofenac can have an impact on your free T4 levels. Besides these, severe cases of chronic ailments, such as liver cirrhosis or chronic kidney failure, can also affect the results of a Free T4 test.
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Thyroxine - Free test price for other cities

Price inKolkataRs. 200
Price inBangaloreRs. 200
Price inMumbaiRs. 200
Price inGurgaonRs. 200
Price inHyderabadRs. 200
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  1. Thyroid Function Tests [Internet]. Alexandria, VA: American Thyroid Association; [Accessed 07 Feb. 2023]. Available from: https://www.thyroid.org/thyroid-function-tests/External Link
  2. Free and Bound Triiodothyronine (Blood) [Internet]. NY: University of Rochester Medical Center; [Accessed 07 Feb. 2023]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=167&ContentID=t3_free_and_bound_bloodExternal Link
  3. Thyroid Function Test [Internet]. Scotland: British Thyroid Foundation; 2021 [Accessed 07 Feb. 2023]. Available from: https://www.btf-thyroid.org/thyroid-function-testsExternal Link
  4. Block-Galarza J. Thyroid Function Tests [Internet]. Alexandria, VA: American Thyroid Association. [Accessed 07 Jul. 2023]. Available from: https://www.thyroid.org/patient-thyroid-information/ct-for-patients/december-2018/vol-11-issue-12-p-3-4/#:~:text=Most%20commonly%2C%20biotin%20use%20can,hormone%20dose%20is%20too%20highExternal Link
  5. Thyroid Tests [Internet]. NIDDK; May 2017 [Accessed 07 Feb. 2023]. Available from: https://www.niddk.nih.gov/health-information/diagnostic-tests/thyroidExternal Link
  6. Adhimoolam M, Arulmozhi R. Effect of antiepileptic drug therapy on thyroid hormones among adult epileptic patients: An analytical cross-sectional study. J Res Pharm Pract. 2016 Jul-Sep;5(3):171-4. [Accessed 07 Jul. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4966235/External Link
  7. Dong BJ. How medications affect thyroid function. West J Med. 2000 Feb;172(2):102-6. [Accessed 09 Feb. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1070767/External Link


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