FT3 & FT4 (Free T3 & Free T4)
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 (FT3) and thyroxine (FT4) 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 hormones like thyroxine (T4) and triiodothyronine (T3), which are responsible for regulating metabolism and other bodily functions. The production and release of these hormones are controlled by the pituitary gland's thyroid-stimulating hormone (TSH). FT4 and FT3 represent the free or unbound, active forms of thyroxine and triiodothyronine. It reflects the amount of available thyroid hormone circulating in the blood.
An FT3 & FT4 (Free T3 & Free T4) test is used to assess how well your thyroid gland is working and aid in the diagnosis and management of thyroid disorders, such as an overactive thyroid gland (hyperthyroidism) or an underactive thyroid gland (hypothyroidism). Your doctor may advise this test if you show symptoms suggestive of hyperthyroidism, such as weight loss, nervousness, irritability, increased sweating, and rapid heartbeat, or hypothyroidism, such as weight gain, fatigue, sensitivity to cold, constipation, and dry skin. It is also important for pregnant women to have healthy amounts of thyroid hormones to ensure the healthy development of their babies.
No special preparations are needed for this test. Usually, you do not need to stop taking your thyroid medication before taking this test. However, let your doctor know about all your medications, as some can affect thyroid function. 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?
Contains 2 testsAn 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 of the 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 as well as T4 to ensure proper functioning. Measuring free forms of thyroid hormones (FT3 and FT4) gives a better understanding of thyroid function than the bound forms as they are independent of changes in the concentration and the binding properties of the thyroid hormone binding proteins.
Thyroxine - Free
The 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.
Know more about Thyroxine - Free
Triiodothyronine Free
The Triiodothyronine Free test measures the levels of free triiodothyronine (T3), a hormone produced by the thyroid gland. T3 hormone plays a vital role in regulating the body's metabolism, energy levels, and growth & development. It exists in the blood in two forms: free T3 and bound T3. Only a small portion of T3 is free (not bound to proteins) and can be utilized by the body’s tissues. In contrast, more than 99% of T3 is bound to proteins, such as albumin and thyroid-binding globulin (TBG), preventing it from entering the tissues. The body balances bound and free T3 to ensure proper functioning.
Know more about Triiodothyronine Free
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 the Free T3 & Free T4 test done?
Q. Can I take the Free T3 & Free T4 test during pregnancy?
Q. Is fasting required for the Free T3 & Free T4 test?
Q. What happens when T3 and T4 levels are high?
Q. What happens when T3 and T4 levels are low?
Q. What factors can affect the results of the Free T3 & Free T4 test?
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References
- Thyroid Function Tests [Internet]. Alexandria, VA: American Thyroid Association; [Accessed 10 Jul. 2023]. Available from: https://www.thyroid.org/thyroid-function-tests/
- 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_blood
- 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/
- 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%20high
- Thyroid Tests [Internet]. NIDDK; May 2017 [Accessed 10 Jul. 2023]. Available from: https://www.niddk.nih.gov/health-information/diagnostic-tests/thyroid
- 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/
- 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/
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