free testosterone
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Indications
- evaluation of testosterone concentrations in clinical states in which sex hormone-binding globulin (SHBG) may be altered
- decreased serum SHBG
- obesity, diabetes mellitus, nephrotic syndrome, hypothyroidism, acromegaly, & in patients taking steroids or progestins []
- increased serum SHBG
- older age, HIV1 infection, cirrhosis & hepatitis, hyperthyroidism, hyperestrogenic states (pregnancy oral contraceptives) & in patients taking certain anticonvulsants 12]
- decreased serum SHBG
- adolescent polycystic ovary syndrome[2]
- measurement of free testosterone before & after dexamethasone administration may use useful
- relatively few conditions in which free testosterone is necessary (total testosterone is generally sufficient)
- levels < 150 ng/dL or > 350 ng/dL identify or exclude biochemical hypogonadism reasonably accurately
- when levels fall between these thresholds, consider serum free testosterone[3]
Reference interval
Principle
- free testosterone is probably the physiologically active form of testosterone
- only 1-3% of circulating testosterone is in the free form; most is bound to SHBG
- there is also non-specific binding to albumin
- albumin-bound testosterone may be physiologically active
- bioavailable testosterone measures free plus albumin-bound testosterone
Increases
females:
- polycystic ovary syndrome (female)
Decreases
males
- hypogonadism
- orchidectomy
- estrogen therapy
- Klinefelter's syndrome
- hypopituitarism
- testicular feminization
- hepatic cirrhosis
- andropause*
- levels drop in men with children
* 40% of men > 45 years of age[4]
Specimen
- serum (red top); separate serum; store frozen
- plasma (green top) {heparin}; separate plasma; store frozen
Notes
- female athletes with higher free testosterone tended to perform better in competitive events[11]
More general terms
More specific terms
Additional terms
- bioavailable testosterone
- testosterone (Delatestryl Testopel, Striant, Intrinsa, Xyosted)
- testosterone in serum
References
- ↑ ABC's of Interptretive Laboratory Data, 4th ed, Bakerman S et al (eds), Interpretive Laboratory Data Inc, Scottsdale, AZ, 2003 http://www.bakermanbooks.com
- ↑ 2.0 2.1 Moll GW et al, J Pediatrics 102:461, 1983
- ↑ 3.0 3.1 Anawalt BD et al. Performance of total testosterone measurement to predict free testosterone for the biochemical evaluation of male hypogonadism. J Urol 2012 Apr; 187:1369. PMID: https://www.ncbi.nlm.nih.gov/pubmed/22341266
- ↑ 4.0 4.1 Panel of 5 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0070102.jsp
- ↑ Panel of 4 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0070109.jsp
- ↑ Panel of 3 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0070111.jsp
- ↑ Panel of 3 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0081056.jsp
- ↑ Panel of 3 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0081057.jsp
- ↑ Mini Panel of 2 tests: Sex Hormone Binding Globulin 1 . Testosterone, Free LC-MS/MS Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0081059.jsp
- ↑ Panel of 5 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0000000.jsp
- ↑ 11.0 11.1 Monaco K Androgens Linked to Competitive Edge in Female Athletes - Higher free testosterone levels tied to better performance in stamina, visuospatial events MedPage Today. July 03, 2017 https://www.medpagetoday.com/Endocrinology/Steroids/66402
- ↑ Sargis RM, Davis AM Evaluation and Treatment of Male Hypogonadism. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. JAMA. Published online March 17, 2018. PMID: https://www.ncbi.nlm.nih.gov/pubmed/29550857 https://jamanetwork.com/journals/jama/fullarticle/2675569