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Thyroid.org describes the thyroid gland as a butterfly-shaped gland located in the lower front of the neck. It makes hormones that help each cell in the body to work right. Thyroid function tests are used to tell how well the thyroid is working 1. They are used to help diagnose hypothyroid, or underactive function; hyperthyroid, or overactive function; and to monitor response to thyroid medications 1.
T3 Blood Test
Triiodothyronine, or T3, plays an important, active role in metabolism. T3 is normally present in very small amounts, but has a significant impact. The range for normal values is 100 to 200 nanograms per deciliter, according to Medline Plus. Greater-than-normal values may be due to hyperthyroidism, thyroid cancer or high levels of a protein that carries T3 in the blood. Lower-than-normal values may indicate hypothyroidism, starvation or a long illness.
- Triiodothyronine, or T3, plays an important, active role in metabolism.
- Greater-than-normal values may be due to hyperthyroidism, thyroid cancer or high levels of a protein that carries T3 in the blood.
T4 Blood Test
Uses of the Radioactive Iodine 131
Thyroxine is also known as T4 because it contains four iodine atoms, according to thyroid.com. Most T4 is transported in the bloodstream by proteins, and the liver converts T4 into T3. A typical normal range, says Medline Plus, is 4.5 to 11.2 micrograms per deciliter. If higher, it can indicate hyperthyroidism, or Graves disease; toxic goiter; or thyroiditis. Lower levels may involve such conditions as hypothyroidism, malnutrition or use of certain medications.
- Thyroxine is also known as T4 because it contains four iodine atoms, according to thyroid.com.
- If higher, it can indicate hyperthyroidism, or Graves disease; toxic goiter; or thyroiditis.
TSH Blood Test
TSH, or thyroid stimulating hormone, is produced by the pituitary gland and tells the thyroid gland to produce and release T3 and T4, says Medline Plus 1. Normal lab values are 0.4 to 4.0 milliliters per deciliter; this range is less if under treatment for a thyroid disorder, at 0.5 to 3.0 milliliters per deciliter. A high level means the thyroid gland is failing, or hypothyroidism. In the opposite situation, when the TSH level is low, hyperthyroidism is indicated. Occasionally, a low TSH level may result from an abnormality in the pituitary gland.
- TSH, or thyroid stimulating hormone, is produced by the pituitary gland and tells the thyroid gland to produce and release T3 and T4, says Medline Plus 1.
- Occasionally, a low TSH level may result from an abnormality in the pituitary gland.
What Is a Normal T4 Thyroid Level?
Medline Plus reports that “a thyroid scan is a nuclear medicine exam that uses a radioactive iodine tracer to see how well the thyroid gland is working.” A radioactive iodine pill is swallowed; the thyroid gland is scanned four to six hours later to detect the amount of iodine absorbed and to observe a “picture” of the thyroid 1. In a normal scan, the thyroid appears the correct size, shape and in the proper location. Hypothyroidism is suspected if less than the normal amount of iodine is absorbed, and hyperthyroidism if there is higher-than-normal iodine absorption.
Thyroid Gland Function
A description of thyroid function is given by thyroid.org in that the thyroid gland and the pituitary gland act like a heater and a Thermostat in the body 1. The amount of TSH that the pituitary sends into the bloodstream depends on the recognized amount of T4 from the thyroid. More TSH is released if very little T4 is recognized. When the T4 in the bloodstream rises above a certain level, the pituitary production of TSH is shut off.
- A description of thyroid function is given by thyroid.org in that the thyroid gland and the pituitary gland act like a heater and a Thermostat in the body 1.
- The amount of TSH that the pituitary sends into the bloodstream depends on the recognized amount of T4 from the thyroid.
Uses of the Radioactive Iodine 131
What Is a Normal T4 Thyroid Level?
What Does a High TSH Level Mean?
Low Iodine Levels & Panic Attacks
What Are the Causes of Fluctuating Thyroid Levels?
Niacin & Thyroid Disease
Cytomel Thyroid T3/T4 for Weight Loss
Iodine's Effect on Calcium Absorption
What Do CBC, CMP & TSH Test Results Mean?
What Does Low TSH Level Mean?
- Medline Plus: Thyroid Function Tests
- 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
Rhonda Merritt started freelance writing in 2010. She is a registered nurse specializing in cardiac rehabilitation and cardiac care. Merritt has her personal fitness coach certification and is a certified CPR instructor. She holds a Bachelor of Science in nursing. Merritt graduated from Edinboro University in 1988.