Thyroxine - Free
Understanding Thyroxine - Free
What is Thyroxine - Free?
The 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).
The 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?
The Thyroxine - Free test is done:
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To measure the levels of free T4 hormone in the body.
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As part of a thyroid profile test along with FT3 and TSH tests.
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To evaluate symptoms suggestive of an imbalance in thyroid hormone levels, such as fatigue, weight loss, hair loss, and changes to heart rate.
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To diagnose and monitor the treatment of hypothyroidism or hyperthyroidism.
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To detect an underactive thyroid gland in newborn babies.
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To evaluate other disorders, such as thyroid nodules, goiters, and pituitary or hypothalamus gland disorders.
What does Thyroxine - Free measure?
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.
Interpreting Thyroxine - Free results
Interpretations
|
Age |
FT4 (pmol/L) |
|
Newborn |
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 |
|
Adults |
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.
Frequently Asked Questions about Thyroxine - Free
Q. Why is the Thyroxine - Free test done?
Q. Can I take the Thyroxine - Free test during pregnancy?
Q. What do high T4 levels signify?
Q. What happens when the T4 level is low?
Q. How can I reduce my T4 levels naturally?
Q. Is fasting required for the Free T4 test?
Q. What factors can affect the test results of the Free T4 test?
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References
- Thyroid Function Tests [Internet]. Alexandria, VA: American Thyroid Association; [Accessed 07 Feb. 2023]. Available from: https://www.thyroid.org/thyroid-function-tests/
- 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_blood
- Thyroid Function Test [Internet]. Scotland: British Thyroid Foundation; 2021 [Accessed 07 Feb. 2023]. Available from: https://www.btf-thyroid.org/thyroid-function-tests
- 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%20high
- Thyroid Tests [Internet]. NIDDK; May 2017 [Accessed 07 Feb. 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 07 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 09 Feb. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1070767/
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