At a Glance
Why Get Tested?
When to Get Tested?
For screening: There is no consensus within the medical community as to the age adult screening should begin or whether screening should be done; however, newborn screening is widely recommended.
For monitoring treatment: as directed by your doctor
Otherwise: when a person has symptoms of hyperthyroidism or hypothyroidism and/or an enlarged thyroid
A blood sample drawn from a vein in the 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 doctor about any drugs that you are taking.
The Test Sample
What is being tested?
This test measures the amount of thyroid-stimulating hormone (TSH) in the blood. TSH is produced by the pituitary gland, a tiny organ located below the brain and behind the sinus cavities. It is part of the body's feedback system to maintain stable amounts of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) in the blood. Thyroid hormones help control the rate at which the body uses energy. When concentrations decrease in the blood, the hypothalamus releases thyrotropin releasing hormone (TRH). This stimulates the release of TSH by the pituitary gland. The TSH in turn stimulates the production and release of T4 and T3 by the thyroid gland, a small butterfly-shaped gland that lies in the neck flat against the windpipe. When all three organs are functioning normally, thyroid production turns on and off to maintain constant blood thyroid hormone levels.
If there is pituitary dysfunction, then increased or decreased amounts of TSH may result. When TSH concentrations are increased, the thyroid will make and release inappropriate amounts of T4 and T3 and the affected person may experience symptoms associated with hyperthyroidism, such as rapid heart rate, weight loss, nervousness, hand tremors, irritated eyes, and difficulty sleeping. If there is decreased production of thyroid hormones (hypothyroidism), the person may experience symptoms such as weight gain, dry skin, constipation, cold intolerance, and fatigue. In addition to pituitary dysfunction, hyperthyroidism or hypothyroidism can occur if there is a problem with the hypothalamus (insufficient or excessive TRH). Thyroid hormone levels may also be altered by a variety of thyroid diseases regardless of the amount of TSH present in the blood.
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 doctor about any drugs that you are taking.
Ask a Laboratory Scientist
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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
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.
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.