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TSH

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Also known as: Thyrotropin
Formal name: Thyroid-stimulating Hormone

At a Glance

Why Get Tested?

To screen for and help diagnose thyroid disorders; to monitor treatment of hypothyroidism and hyperthyroidism

When to Get Tested?

For screening: Newborn screening is widely recommended; however, there is no consensus within the medical community as to the age adult screening should begin or whether screening should be done.
For monitoring treatment: as directed by your healthcare provider
Otherwise: when a person has symptoms of hyperthyroidism or hypothyroidism and/or an enlarged thyroid

Sample Required?

A blood sample drawn from a vein in your arm or from pricking the heel of an infant

Test Preparation Needed?

None needed; however, certain medications can interfere with the TSH test, so tell your health practitioner about any drugs that you are taking. If you take thyroid hormone as treatment for thyroid disease, it is recommended that your blood sample be drawn before you take your dose for that day.

The Test Sample

What is being tested?

Thyroid-stimulating hormone (TSH) is produced by the pituitary gland, a tiny organ located below the brain and behind the sinus cavities. TSH stimulates the thyroid gland to release the hormones thyroxine (T4) and triiodothyronine (T3) into the blood. These thyroid hormones help control the rate at which the body uses energy. This test measures the amount of TSH in the blood.

TSH, along with its regulatory hormone thyrotropin releasing hormone (TRH), which comes from the hypothalamus, is part of the feedback system that the body uses to maintain stable amounts of thyroid hormones in the blood. When thyroid hormone concentrations decrease, the production of TSH by the pituitary gland is increased. TSH in turn stimulates the production and release of T4 and T3 by the thyroid gland, a small butterfly-shaped gland that lies at the base of the throat flat against the windpipe. When all three organs are functioning normally, thyroid production turns on and off to maintain relatively stable levels of thyroid hormones in the blood.

If the thyroid releases inappropriately large amounts of T4 and T3, the affected person may experience symptoms associated with hyperthyroidism, such as rapid heart rate, weight loss, nervousness, hand tremors, irritated eyes, and difficulty sleeping. Graves disease is the most common cause of hyperthyroidism. It is a chronic autoimmune disorder in which the affected person's immune system produces antibodies that act like TSH, leading to the production of excessive amounts of thyroid hormone. In response, the pituitary may produce less TSH, usually leading to a low level in the blood.

If there is decreased production of thyroid hormones by the thyroid (hypothyroidism), the person may experience symptoms such as weight gain, dry skin, constipation, cold intolerance, and fatigue. Hashimoto thyroiditis is the most common cause of hypothyroidism in the U.S. It is a chronic autoimmune condition in which the immune response causes inflammation and damage to the thyroid as well as the production of autoantibodies. With Hashimoto thyroiditis, the thyroid produces low levels of thyroid hormone. The pituitary may produce more TSH, usually resulting in a high level in the blood.

However, the level of TSH does not always predict or reflect thyroid hormone levels. Some people produce an abnormal form of TSH that does not function properly. They often have hypothyroidism despite having normal or even mildly elevated TSH levels. In a variety of thyroid diseases, thyroid hormone levels may be high or low, regardless of the amount of TSH present in the blood.

Rarely, pituitary dysfunction may result in increased or decreased amounts of TSH. In addition to pituitary dysfunction, hyperthyroidism or hypothyroidism can occur if there is a problem with the hypothalamus (insufficient or excessive TRH).

How is the sample collected for testing?

A blood sample is obtained from a needle placed in a vein in the arm or from pricking the heel of an infant.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed. Certain medications can interfere with the TSH test, so tell your health practitioner about any drugs that you are taking. If you take thyroid hormone as treatment for thyroid disease, it is recommended that your blood sample be drawn before you take your dose for that day.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

(Updated 2014 May 14). Thyroid Tests. National Endocrine and Metabolic Diseases Information Service [On-line information]. Available online at http://endocrine.niddk.nih.gov/pubs/thyroidtests/index.aspx through http://endocrine.niddk.nih.gov. Accessed June 2014.

Topiwala, S. (Updated 2012 June 26). TSH test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003684.htm through http://www.nlm.nih.gov. Accessed June 2014.

(© 1995–2014). Thyroid-Stimulating Hormone-Sensitive (s-TSH), Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8939 through http://www.mayomedicallaboratories.com. Accessed June 2014.

Lin, J. (Updated 2012 February 17). Thyroid-Stimulating Hormone. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2074091-overview through http://emedicine.medscape.com. Accessed June 2014.

Meikle, A. W. and Straseski, J. (Updated 2014 April). Thyroid Disease. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/ThyroidDz.html?client_ID=LTD through http://www.arupconsult.com. Accessed June 2014.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 949-950.

McPherson, R. and Pincus, M. (© 2011). Henry's Clinical Diagnosis and Management by Laboratory Methods 22nd Edition: Elsevier Saunders, Philadelphia, PA. Pg 376.

©2014 American Thyroid Association. Hyperthyroidism and Other Causes of Thyrotoxicosis: Management Guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. If antithyroid drugs are chosen as initial management of GD, how should the therapy be managed? Available online at http://www.thyroid.org/thyroid-guidelines/hyperthyroidism/resultse/ through http://www.thyroid.org. Accessed September 2014.

(April 4, 2014) Aytug S. Euthyroid Sick Syndrome. Medscape. Available online at http://emedicine.medscape.com/article/118651-overview through http://emedicine.medscape.com. Accessed September 2014.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

U.S. Preventive Services Task Force (2004 May 15). Screening for Thyroid Disease: Recommendation Statement. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20040515/us.html through http://www.aafp.org.

MedlinePlus Medical Encyclopedia. TSH. (Updated 10/24/07). [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003684.htm.

(© 2005). Thyroid Stimulating Hormone (TSH). ARUP's Guide to Clinical Laboratory Testing [On-line information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_239b.jsp#1149154 through http://www.aruplab.com.

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp. 1038-1041.

Ladenson,PW et al, for the American Thyroid Association. American Thyroid Association guidelines for detection of thyroid dysfunction. 12 Jun 2000. Arch Intern Med 60:1573-1575.

American Association of Clinical Endocrinologists. Women's endocrine health. Available online at http://www.powerofprevention.com/w_endocrine.php through http://www.powerofprevention.com.

Eckman, A. (Updated 2010 April 19). TSH test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003684.htm. Accessed February 2011.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 949-950.

Meikle, A. and Roberts, W. (Updated 2010 October). Thyroid Disease. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/ThyroidDz.html through http://www.arupconsult.com. Accessed February 2011.

(© 2008). Thyroid Function Tests. American Thyroid Association [On-line information]. Available online at http://www.thyroid.org/patients/patient_brochures/function_tests.html through http://www.thyroid.org. Accessed February 2011.

Bissell, M. Editor (2010 August). Lower thyroid-stimulating hormone thresholds in neonatal screening. CAP Today. Clinical Abstracts [On-line information]. Available online through http://www.cap.org. Accessed February 2011.

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