Testosterone Tests

Testosterone Components

Total Testosterone

The measurement of free testosterone, albumin bound testosterone and Sex Hormone Binding Globulin bound testosterone.

Free Testosterone

The measurement of freely circulating testosterone.  Free testosterone is a calculated test.  After measuring the total testosterone, albumin and SHBG, a mathematical formula is used to subtract albumin-bound and SHBG-bound testosterone, leaving the calculated free testosterone level.

Bioavailable Testosterone

This is the fraction of circulating testosterone that readily enters cells.  Testosterone does not bind strongly to albumin and, the binding is easily reversed.  Bioavailable then is the Free Testosterone plus the albumin-bound testosterone.  After measuring the total testosterone, albumin and SHBG, a mathematical formula is used to subtract SHBG-bound testosterone, leaving the calculated bio-available testosterone level.

Clinical Significance

The measurement of circulating testosterone is relevant in the investigation of androgen disorders in men, women and children.

Men

In men, testosterone analysis is used to evaluate endocrine activity of the testes.  It is also used for diagnosis of testosterone deficiency.  This test could be ordered for several reasons including:  suspected infertility, decreased sex drive, erectile dysfunction, lack of beard and body hair, decreased muscle mass and gynecomastia.  Measurement of testosterone is also recommended in monitoring patients with metastatic prostate cancer treated with gonadotropin-releasing hormone analogs or by antiandrogen therapy and, as a means for checking testosterone levels have dropped to extremely low levels.

Women

For women, testosterone is often measured as part of investigation of irregular or no menstrual periods, alopecia, acne and hirsutism.  Testosterone levels can rise because of polycystic ovarian syndrome (PCOS) and testosterone measurement can aid in the diagnosis of PCOS.  Testosterone measurement can also be used for detection of androgen-secreting tumors or to determine the minimum drug dose required to suppress androgen secretion in hyperandrogenic women.

Children

Testosterone concentration is measured for the diagnosis, treatment, and gender assignment of newborns or young infants with ambiguous genitalize.  The testosterone concentration can also be used to determine pubertal stage (Tanner Stage) in association with physical examination in the follow-up of children with precocious or delayed puberty.  Testosterone is also closely monitored for patients diagnosed with 21-hyperoxylase deficiency resulting in congenital adrenal hyperplasia.

Clinical Background

About 60% of circulating testosterone is strongly bound to Sex Hormone-Binding Globulin (SHBG), and about 40% of the hormone is bound to albumin.  Normally, only 1 – 4% exists as free testosterone.

 

Historically, on the free testosterone was thought to be the biologically active component.  However, testosterone that is weakly bound to serum albumin will freely dissociate in the capillary bed, and become readily available for tissue uptake.  So, all non-SHBG bound testosterone is considered bioavailable.

 

References

1.   Manni A, Pardridge WM, Cefalu W, et al: Bioavailability of albumin-bound testosterone. J Clin Endocrinol Metab 1985;61:705

2.   New MI, Josso N: Disorders of gonadal differentiation and congenital adrenal hyperplasia. Endocrinol Metab Clin North Am 1988;17:339-366

3.   Dumesic DA: Hyperandrogenic anovulation: a new view of polycystic ovary syndrome. Postgrad Obstet Gynecol 1995 June;15(13)

4.   Morley JE, Perry HM 3rd: Androgen deficiency in aging men: role of testosterone replacement therapy. J Lab Clin Med 2000;135:370-378

5.   Ankarberg-Lindgren C, Norjavaara E. Estradiol in pediatric endocrinology. Am J Clin Pathol. 2009; 132 (6) :978-980.

6.   Bloomfield D. Secondary amenorrhea. Pediatr Rev. 2006; 27 (3) :113-114.

7.   Goswami D, Conway GS. Premature ovarian failure. Hum Reprod Update. 2005; 11 (4) :391-410.

8.   Heiman DL. Amenorrhea. Prim Care. 2009; 36 (1) :1-17, vii.

9.   Master-Hunter T, Heiman DL. Amenorrhea: evaluation and treatment. Am Fam Physician. 2006; 73 (8) :1374-1382.

10.Practice Committee of the American Society for Reproductive Medicine Current evaluation of amenorrhea. Fertil Steril. 2008; 90 (5 Suppl):S219-S225.

11.Rebar RW. Premature ovarian failure. Obstet Gynecol. 2009; 113 (6) :1355-1363.

12.Rudolph LM. Cytogenetics of Infertility. In Gersen SL Keagle MB, eds. The Principles of Clinical Cytogenetics. Totowa, New Jersey: Humana Press Inc, 2005. pp. 247-265.

13.Warren MP, Hagey AR. The genetics, diagnosis and treatment of amenorrhea. Minerva Ginecol. 2004; 56 (5) :437-455.

14.Wilson GR, Haddad JE, Haddad CJ. Amenorrhea: common causes and evaluation. Compr Ther. 2005; 1 (4) :270-278. 15. http://labtestsonline.org/

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