EagleBio Spotlight: Free Testosterone



is a steroid hormone from the
androgen group and is predominantly secreted in the testes of males and the
ovaries of females however, there is a small amount of this hormone that is secreted
by the adrenal glands. Testosterone is
the primary male sex hormone as well as an anabolic steroid and it plays key
roles for the health and well-being of both males and females.

Only a small percentage of circulating testosterone
exists as unbound or free testosterone. In fact, testosterone circulates 98%
protein-bound (54% with low affinity to albumin and other proteins, and 44%
with high affinity to SHBG) with only 2% circulating as free testosterone. The
portion which is unbound, referred to as free testosterone, is considered the
component that has the ability to enter cells and in turn, has androgenic
effects. Thus, for these reasons it is proposed that free testosterone will
relate to the biological effect on tissue more than the total testosterone.


Reasons to
Measure Free Testosterone

It is important to measure Free Testosterone for detecting
and monitoring various conditions and diseases that affect both men and women.
Free testosterone is responsible for sexual traits and health problems can
result from elevated or decreased levels of this hormone. As mentioned above, the measurement of the
free or unbound fraction of serum testosterone provides a means of estimating
the physiologically bioactive hormone.


Free Testosterone has been associated
with many diseases and disorders/conditions


Primary and secondary hypogonadism- A failure of the gonads, testes in men and ovaries in
women, to function properly (i.e. primary– direct failure of gonad and secondary
indirect failure of gonad due to problem in the hypothalamus or the pituitary

Delayed or advanced puberty


Loss of sex drive

Bone loss


Cushing Syndrome



Hirsutism– excessive

biological development of sex differences- changes that make the female body
different from a male body- masculization occurs) due to tumors

Polycystic ovaries –Polycystic ovary syndrome (PCOS)
a condition discerned by infertility, lack of menstruation, acne, and excessive
hair growth, particularly on the face

Androgenital syndromes

Cushing Syndrome



1. Alan, Carolyn et. al. “Age-related changes in testosterone and the role of replacement therapy in older men.” Clinical Endocrinology. 2004; 60:6:653–670. 

2.Rosner W, Auchus RJ, Azziz R, et al. “Position statement: Utility, limitations, and pitfalls in measuring testosterone: an Endocrine Society Position Statement”. J Clin Endocrinol Metab. 2007;92:405-413. 

3. Sodergard, R et al. “Calculation of free and bound fractions of testosterone and estradiol-17 beta to human plasma proteins at body temperature”. Journal of Steroid Biochemistry. 1982; 16, 801–810. 


Related Kits:

Steroid Assay Kits

Free Testosterone ELISA Assay Kit

Testosterone ELISA Assay Kit

Testosterone Saliva ELISA Assay Kit

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