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Home›FT3 & FT4 (Free T3 & Free T4).
Test Detail
Understanding the Test
Test Measures
FAQ's
References
Other Tests
Content created by
Written by
Reviewed by
Dr. Anupriya Nautiyal
MD Pathology, MBBS
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FT3 & FT4 (Free T3 & Free T4).

Also known as Free T3 & Free T4
You need to provide
Blood
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 FT3 & FT4 (Free T3 & Free T4).

What is FT3 & FT4 (Free T3 & Free T4).?

An FT3 & FT4 (Free T3 & Free T4). test measures the amount of free form of triiodothyronine (T3) and thyroxine (T4) hormones in the blood. This test helps evaluate the functioning of the thyroid gland and detect possible thyroid disorders, including hyperthyroidism and hypothyroidism.

The thyroid gland is a butterfly-shaped organ in the neck that produces the hormones thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolism and other bodily functions. T3 and T4 circulate in the blood in two forms: bound form (attached to proteins) and free form (does not attach to any protein). The production and release of these hormones are controlled by the thyroid-stimulating hormone (TSH) produced by the pituitary gland. 

Deranged levels of T3 and T4 hormones can result in either hyperthyroidism (a condition in which the thyroid gland produces too much T3 and T4 hormones) or hypothyroidism (a condition in which the thyroid gland produces less T3 and T4 hormones). Your doctor may advise an FT3 & FT4 (Free T3 & Free T4). test if you show symptoms suggestive of hyperthyroidism, such as increased appetite, weight loss, sweating, anxiety, tremors, etc., or hypothyroidism, such as 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, inform your doctor about all your medicines, as some can affect your thyroid function test results. Biotin (Vitamin B7) is a commonly taken over-the-counter supplement that can lead to some aberrancy in your test results even when the values are normal. Therefore, avoid taking biotin two days before an FT3 & FT4 test.

Test result ranges are approximate and may differ slightly between 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, recommend 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 FT3 & FT4 (Free T3 & Free T4). used for?

An FT3 & FT4 (Free T3 & Free T4). test is done:

  • To measure the levels of free T3 and T4 hormones in the body.

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

  • 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 FT3 & FT4 (Free T3 & Free T4). measure?

An FT3 & FT4 (Free T3 & Free T4). test measures the free form of triiodothyronine (FT3) and thyroxine (FT4) hormones made by the thyroid gland. These hormones exist in the blood in two forms: bound (attached to proteins) and free (not attached to proteins). Most T3 and T4 hormones circulating in the blood are bound to proteins, and only a small part circulates freely and constitutes the physiologically active form. The body maintains a delicate balance of bound and free T3 and T4 to ensure proper functioning. 

Answers to Patient Concerns & Frequently Asked Questions (FAQs) about FT3 & FT4 (Free T3 & Free T4).

Frequently Asked Questions about FT3 & FT4 (Free T3 & Free T4).

Q. Why is an FT3 & FT4 (Free T3 & Free T4). test done?

An FT3 & FT4 (Free T3 & Free T4). test is done to check for hyperthyroidism or hypothyroidism when you show symptoms like weight gain/loss, fatigue, dry skin, hair thinning, slow heart rate, muscle weakness, anxiety, trouble sleeping, or frequent bowel movement.

Q. Can I take an FT3 & FT4 (Free T3 & Free T4). test during pregnancy?

Yes, you can take an FT3 & FT4 (Free T3 & Free T4). test during pregnancy. This test is usually recommended along with some other tests during pregnancy to measure the levels of thyroid hormones as their deranged levels can complicate pregnancy.

Q. What happens when T3 and T4 levels are high?

High T3 and T4 levels can lead to a condition called hyperthyroidism. Some of the common causes of hyperthyroidism include nodular goiter and thyroiditis.

Q. What happens when T3 and T4 levels are low?

Low T3 and 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. Is fasting required for an FT3 & FT4 (Free T3 & 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 results of an FT3 & FT4 (Free T3 & Free T4). test?

Certain medications like methadone, birth control pills, or steroids can affect your free T3 levels. Similarly, phenobarbital, amiodarone, or diclofenac can have an impact on your free T4 levels. Besides this, severe cases of chronic ailments, such as liver cirrhosis or chronic kidney failure, can also affect your FT3 and FT4 test results.
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References

  1. Thyroid Function Tests [Internet]. Alexandria, VA: American Thyroid Association; [Accessed 10 Jul. 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 10 Jul. 2023]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=167&ContentID=t3_free_and_bound_bloodExternal Link
  3. Welsh KJ, Soldin SJ. Diagnosis of endocrine disease: How reliable are free thyroid and total T3 hormone assays?. Eur J Endocrinol. 2016 Dec;175(6):R255-R263. [Accessed 10 Jul. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5113291/External Link
  4. Block-Galarza J. Thyroid Function Tests [Internet]. Alexandria, VA: American Thyroid Association. [Accessed 10 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 10 Jul. 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 10 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 10 Jul. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1070767/External Link

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