The thyroid is the gland in your body that regulates metabolism. It produces two hormones--T4 and T3. The normal reading for the Total T4 is considered to be between 4 and 11. However, the T4 level alone does not indicate whether you have a thyroid problem. The test must be combined with a test for TSH (thyroid stimulating hormone).
Since your thyroid regulates your metabolism, symptoms of an overactive thyroid include sleeplessness, irritability, nervousness, weight loss and increased bowel movements. Symptoms of an underactive thyroid include fatigue, weight gain and lack of motivation. A test outside of the normal ranges may also indicate thyroid cancer.
What Is T4
T4 is a thyroid hormone that has four iodine units. Iodine is used by the thyroid in production of thyroid hormone and is ingested through the foods we eat. There is more T4 in your body than T3, but it is T3 that is the active hormone.
Niacin & Thyroid Disease
If you believe you have a thyroid issue, ask your physician to recommend a specialist, known as an endocrinologist. These doctors specialize in issues with the endocrine glands (hormone-production glands) and are better equipped to help you manage a thyroid problem than a general practice physician. He or she will test your T4 thyroid levels as well as T3 and TSH.
If you suspect that you have an overactive thyroid, your T4 thyroid level and TSH hormones may be tested simultaneously. Your physician may order a test called Total T4 or Total Thyroxine. If the results show that your Total T4 thyroid level is above the normal range (4-11) and that your TSH is below the normal range (.5-5.5), then you may have an overactive thyroid. This is also called hyperthyroidism.
Using a test called Free T4, the normal range is .8-1.8. If your test indicates T4 thyroid level is above 1.8, you may have an overactive thyroid.
- If you suspect that you have an overactive thyroid, your T4 thyroid level and TSH hormones may be tested simultaneously.
- If your test indicates T4 thyroid level is above 1.8, you may have an overactive thyroid.
Normal Range for Thyroid Level
Using the Total T4, test results that show your T4 thyroid level is below the normal range (4-11) and that your TSH is above the normal range indicate an underactive thyroid. This is known as hypothyroidism.
Using the Free T4 test, if your result is less than .8, then you may have an underactive thyroid 1.
If you are diagnosed with an overactive thyroid, treatments include drug therapy, surgery or radioactive iodine. The latter two will reduce the size of the thyroid gland, in turn reducing the amount of T4 output. Drug therapies may help to inhibit the production of thyroid hormones, but are not usually considered a long-term solution. With the surgical option, all or part of the thyroid is removed. With the radioactive iodine option, you will ingest the radioiodine and, over the course of weeks or months, it will destroy all or part of the thyroid. Neither the surgical option nor the radioiodine option is an exact science and many patients end up with an underactive thyroid, which is then regulated through medication.
If you are diagnosed with an underactive thyroid (or end up that way after removal of the thyroid gland), you will be prescribed a hormone replacement drug that is to be taken daily for the rest of your life.
- If you are diagnosed with an overactive thyroid, treatments include drug therapy, surgery or radioactive iodine.
- Neither the surgical option nor the radioiodine option is an exact science and many patients end up with an underactive thyroid, which is then regulated through medication.
Niacin & Thyroid Disease
Normal Range for Thyroid Level
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Diet Menu Plan for an Underactive Thyroid
What Does Low TSH Level Mean?
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- Thyroid Test Result Lab Values
- American Thyroid Association. General Information/Press Room.
- Pirahanchi Y, Jialal I. Physiology, Thyroid Stimulating Hormone (TSH). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Updated April 25, 2019.
- AACC. Hashimoto Thyroiditis. Lab Tests Online. Updated October 18, 2019.
- DeGroot LJ. Graves’ Disease and the Manifestations of Thyrotoxicosis. [Updated 2015 Jul 11]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2015.
- Nguyen QT, Lee EJ, Huang MG, Park YI, Khullar A, Plodkowski RA. Diagnosis and treatment of patients with thyroid cancer. Am Health Drug Benefits. 2015;8(1):30-40.
- Bindra A, Braunstein GD. Thyroiditis. Am Fam Physician. 2006;73(10):1769-76.
- Medeiros-Neto G. Multinodular Goiter. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-. Updated September 26, 2016.
- The National Institute of Diabetes and Digestive and Kidney Diseases. Hypothyroidism (Underactive Thyroid). Published August 2016.
- The National Institute of Diabetes and Digestive and Kidney Diseases. Hyperthyroidism (Overactive Thyroid). Published August 2016.
- Brent GA. Environmental exposures and autoimmune thyroid disease. Thyroid. 2010;20(7):755-61. doi:10.1089/thy.2010.1636
- Mcaninch EA, Bianco AC. The history and future of treatment of hypothyroidism. Ann Intern Med. 2016;164(1):50-6. doi:10.7326/M15-1799
- The National Institute of Diabetes and Digestive and Kidney Diseases. Grave’s Disease. Published September 2017.
- Stagnaro-Green, A., Abalovich, M, Alexander, E. et. al. Guidelines of the American thyroid association for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid. 2011(21)10. doi:10.1089/thy.2011.0087
- Liu G, Liang L, Bray GA, et al. Thyroid hormones and changes in body weight and metabolic parameters in response to weight loss diets: the POUNDS LOST trial. Int J Obes (Lond). 2017;41(6):878-886. doi:10.1038/ijo.2017.28
- Bahn R, Burch H, Cooper D, et al. Hyperthyroidism and other causes of thyrotoxicosis: Management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. Endocrine Practice. 2011;17(3). doi:10.1089/thy.2010.0417
- Braverman L, Cooper D. Werner & Ingbar's The Thyroid, 10th Edition. WLL/Wolters Kluwer; 2012.
- Garber J, Cobin R, Gharib H, et. al. Clinical practice guidelines for hypothyroidism in adults: Cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocrine Practice. 2012;18(6). doi:10.1089/thy.2012.0205
- Haugen A, Alexander K., Bible K, et. al. 2015 American Thyroid Association Management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2016;26(1):1-133. doi:10.1089/thy.2015.0020
- Smallridge R, Ain K, Asa S, et. al. American Thyroid Association guidelines for management of patients with anaplastic thyroid cancer. Thyroid. 2012;22(11). doi:10.1089/thy.2012.0302
- Wells, S, Asa S, Dralle H, et. al. Revised American Thyroid Association guidelines for the management of medullary thyroid carcinoma. Thyroid. 2015;25(6). doi:10.1089/thy.2014.0335
J.D. Chi is a professional journalist who has covered sports for more than 20 years at newspapers all over the United States. She has covered major golf tournaments and the NFL as well as travel and health topics. Chi received her Bachelor of Arts in professional writing from Carnegie Mellon University and is working toward a master's degree in journalism.