Thyroxine - Total
Understanding Thyroxine - Total
What is Thyroxine - Total?
The Thyroxine - Total is a blood test that measures the level of total thyroxine (T4) hormone in the blood. This test helps assess overall thyroid function and detect possible thyroid disorders. It is also performed in combination with total T3 and TSH tests as part of a thyroid profile total test.
Thyroxine, also known as T4, is a hormone produced by the thyroid gland. The thyroid is a small, butterfly-shaped gland located at the front of your neck. It helps regulate the body’s metabolism, normal temperature, blood pressure, and heart rate. T4 along with triiodothyronine (T3), another hormone produced by the thyroid gland, plays an important role in the growth and development of the nervous system and the brain. T4 exists in the blood in two forms: bound (attached to proteins) and free (not attached to proteins).
The Thyroxine - Total measures the total level (both free and bound forms) of the T4 hormone. Deranged levels of T4 can result in either hyperthyroidism (the thyroid gland produces too much T4) or hypothyroidism (the thyroid gland produces less T4). Your doctor may suggest this test if you show symptoms 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 the Thyroxine - Total test. However, do let your doctor know about all the medications you take as some of those can affect thyroid function. Biotin (Vitamin B7) is a commonly taken over-the-counter supplement that can lead to some aberrancy in your thyroid function test values even if they are normal. Therefore, 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 your overall treatment plan.
What is Thyroxine - Total used for?
The Thyroxine - Total test is done:
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To measure the levels of total T4 hormone in the body.
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As part of a thyroid profile total test along with total T3 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 disorders such as thyroid nodules, goiters, and pituitary or hypothalamus gland disorders.
What does Thyroxine - Total measure?
The Thyroxine - Total test measures both the bound and unbound/free form of thyroxine (T4) hormone in the blood. T4 exists in the blood in two forms: bound (attached to proteins) and free (not attached to proteins). Most of the T4 circulating in the blood is bound to proteins and only a small part is free. It is necessary to maintain a fine balance of these forms to ensure the proper functioning of the body.
Interpreting Thyroxine - Total results
Interpretations
Values higher than normal reference range are seen in hyperthyroidism and patients with acute thyroiditis.
Values lower 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 - Total
Frequently Asked Questions about Thyroxine - Total
Q. Why is the Thyroxine - Total test done?
Q. Can I take the Total T4 test during pregnancy?
Q. Is fasting required for the Total T4 test?
Q. What happens when the Total T4 levels are high?
Q. What happens when the Total T4 levels are low?
Q. What are the factors affecting thyroid hormones?
Q. What is Hyperthyroidism?
Q. What are the symptoms of Hyperthyroidism?
Q. What is Hypothyroidism?
Q. What are the symptoms of Hypothyroidism?
Q. How can hyperthyroidism affect a pregnant woman and her baby?
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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/
- University of Rochester Medical Center. Free and Bound Triiodothyronine (Blood) [Internet]. NY. [Accessed 07 Feb. 2023]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=167&ContentID=t3_free_and_bound_blood
- British Thyroid Foundation. 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
- National Institute of Diabetes and Digestive and Kidney Diseases. Thyroid Tests [Internet]. National Institute of Health; 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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