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Testosterone

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Also known as: Total Testosterone; Free Testosterone; Bioavailable Testosterone
Formal name: Testosterone
Related tests: FSH, LH, SHBG, DHEAS, Estradiol (see Estrogens), DHT, Gonadotropin-releasing Hormone, Semen Analysis, Anti-Mullerian Hormone, Androstenedione

At a Glance

Why Get Tested?

To detect an abnormal testosterone level in males and females; in males, to help diagnose the cause of erectile dysfunction, the inability of your partner to get pregnant (infertility), or premature or delayed puberty; in females, to help diagnose the cause of masculine physical features (virilization), infertility, or polycystic ovary syndrome (PCOS)

When to Get Tested?

For males, when you may be infertile or are unable to get or maintain an erection; when you are a boy with either early or delayed sexual maturity (puberty)
For females, when you have male traits, such as a low voice or excessive body hair (hirsutism), when you have abnormal uterine bleeding, do not menstruate (amenorrhea), or are infertile

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Testosterone is a steroid hormone (androgen) produced by special endocrine tissue (the Leydig cells) in the male testicles. It is also produced by the adrenal glands in both males and females and, in small amounts, by the ovaries in females. This test measures the level of testosterone in the blood.

In males, testosterone stimulates development of secondary sex characteristics, including enlargement of the penis, growth of body hair, muscle development, and a deepening voice. It is present in large amounts in males during puberty and in adult males to regulate the sex drive and maintain muscle mass. In women, testosterone is converted to estradiol, the main sex hormone in females.

Testosterone production is stimulated and controlled by luteinizing hormone (LH), which is manufactured by the pituitary gland. Testosterone works within a negative feedback mechanism: as the testosterone level increases, LH production decreases, which slows testosterone production; decreased testosterone causes increased production of LH, which in turn stimulates testosterone production. Testosterone levels are diurnal, peaking in the early morning hours (about 4:00 to 8:00 am), with the lowest levels in the evening (about 4:00 to 8:00 pm). Levels also increase after exercise and also decrease with age. About two-thirds of testosterone circulates in the blood bound to sex-hormone binding globulin (SHBG) and slightly less than one-third bound to albumin. A small percent (about 1-4%) circulates as free testosterone.

In many cases, measurement of total testosterone provides the doctor with adequate information. However, in certain cases, for example when the level of SHBG is abnormal, a test for free or bioavailable testosterone may be performed as it may more accurately reflect the presence of a medical condition.

How is the sample collected for testing?

A blood sample is taken by needle from a vein in the arm.

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.

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

(June 7, 2012) Kaplowitz. Precocious Puberty. Medscape Reference article. Available online at http://emedicine.medscape.com/article/924002-overview through http://emedicine.medscape.com. Accessed November 2012.

(June 6, 2012) Kemp S. Hypogonadism. Medscape Reference. Available online at http://emedicine.medscape.com/article/922038-overview through http://emedicine.medscape.com. Accessed November 2012.

(October 30, 2012) Lucidi R. Polycystic Ovarian Syndrome. Medscape Reference. Available online at http://emedicine.medscape.com/article/256806-overview through http://emedicine.medscape.com. Accessed November 2012.

The Endocrine Society's Clinical Guidelines. Testosterone Therapy in Adult Men with Androgen Deficiency Syndromes. J Clin Endocrinol Metab June 2010, 95(6):2536–2559. PDF available for download at http://www.endo-society.org/guidelines/final/upload/FINAL-Androgens-in-Men-Standalone.pdf through http://www.endo-society.org. Accessed November 2012.

Harrison's Principles of Internal Medicine, 18ed, Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, Eds., McGraw-Hill. (2012) Chapters 49 & 346.

Sources Used in Previous Reviews

Clinical Chemistry: Theory, Analysis, Correlation. 3rd Edition. Lawrence A. Kaplan and Amadeo J. Pesce, St. Louis, MO. Mosby, 1996.

Clinical Chemistry: Principles, Procedures, Correlations. Michael L. Bishop, Janet L. Duben-Engelkirk, Edward P. Fody. Lipincott Williams & Wilkins, 4th Edition.

The Gale Encyclopedia of Childhood and Adolescence: Testosterone. Available online at http://www.findarticles.com/p/articles/mi_g2602 through http://www.findarticles.com.

Laurence M. Demers, PhD. Distinguished Professor of Pathology and Medicine, The Pennsylvania State University College of Medicine, The M. S. Hershey Medical Center, Hershey, PA.

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, Pp 481-484.

(January 2006) The Hormone Foundation. Low Testosterone and Men's Health. PDF available for download at http://www.hormone.org/Resources/Reproduction/upload/bilingual_Testosterone.pdf through http://www.hormone.org. Accessed January 2009.

(January 2008) Eugster E, Palmert M, eds. The Hormone Foundation. Precocious Puberty. PDF available for download at http://www.hormone.org/Resources/Growth/upload/bilingual_precocious_puberty.pdf through http://www.hormone.org. Accessed January 2009.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders; 2006.

(March 18, 2008) Holt E. MedlinePlus Medical Encyclopedia. Testosterone. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003707.htm. Accessed January 2009.

(December 9, 2008) Mayo Clinic. Male hypogonadism. Available online at http://www.mayoclinic.com/health/male-hypogonadism/DS00300 through http://www.mayoclinic.com. Accessed January 2009.

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