Unbound bioactive sex steroid
Quality and Security
High-quality testing run in a CLIA-certified and CAP-accredited lab in Santa Clara, California.
About Free Testosterone
${ activeTab.tab_content.text }
Loading...
About Free Testosterone
Overview and History
Free testosterone is a steroid androgen, biochemically derived from cholesterol and produced primarily by the gonads and adrenal glands. In blood it exists in equilibrium with testosterone bound to sex hormone–binding globulin (SHBG) and albumin; the unbound fraction is small but readily available to enter cells and activate androgen receptors.
Clinical awareness of the free versus bound hormone concept grew as protein-binding properties were characterized in the mid-20th century. Today the free fraction is valued because it reflects immediate biological availability, complementing measurements of total testosterone, SHBG, and related endocrine markers.
Interpreting Highs and Lows
Higher free testosterone levels may be associated with greater androgen exposure at tissues and can reflect lower SHBG, increased production, or external hormone exposure; they often occur alongside changes in metabolic markers and reproductive hormones. Lower free testosterone levels can reflect reduced production, higher SHBG, aging, certain medications, nutritional or systemic factors, or endocrine shifts and are often associated with lower energy, reduced muscle mass, or changes in libido.
Interpretation of high or low values is most informative when viewed with total testosterone, SHBG, gonadotropins, and metabolic and organ-function markers from the full Foundation Zoomer panel.
Featured Test
Free testosterone is included in the Foundation Zoomer to assess the bioactive portion of androgen signaling within the Hormone Endocrine domain. It helps clarify how sex-hormone balance interacts with metabolic, cardiovascular, and energy-related patterns, guiding providers toward targeted diagnostic questions and individualized monitoring strategies.
Related Articles
When most people think of histamine, they picture allergy symptoms, sneezing, hives, and congestion. But histamine is far more than an allergy molecul...
A common theme among many of my nutrition clients is that despite eating well, staying active, and managing stress, they feel worn down, inflamed, and...
Hormone imbalances are among the most common complaints we hear as functional and integrative medical practitioners. However, many of us are missing a...
.png)
Oxidative stress is a crucial determinant of cellular function and longevity, representing the imbalance between free radicals and antioxidants in the...
Results trusted by over 18,000 functional wellness professionals
We’re the leading provider of specialty wellness lab testing because we develop our testing with rigorous, ongoing research by top clinical experts, doctors, and scientists.
-1.png?width=542&height=427&name=shutterstock_2371998817%201%20(1)-1.png)
.png?width=207&height=108&name=Group%201410104259%20(1).png)
The gold standard of accuracy in the lab industry
Our tests run on a proprietary 3Dense microchip technology platform that boasts unrivaled specificity and sensitivity. While most other labs carry only CLIA certification, we're CAP-accredited by the College of American Pathologists.
.png?width=487&height=356&name=Frame%201410104197%20(3).png)
.png?width=187&height=63&name=category%20Card%20text%20(1).png)
.png?width=202&height=63&name=category%20Card%20text%20(2).png)
Mary Beth Augustine
DCN, RDN, FAND- Lead Clinical Educator
Suzanne Barker
MS, RDN, LD, CTTS, CGP- Clinical Educator
Suzette Garcia
MSc- MHNE- Clinical Educator
Brooke Mader Ganev
MS, CNS, LDN, FDN- Clinical Educator
Adair Anderson
MS, RDN, LDN- Clinical Educator
Lillie Luu Nguyen
DCN, CNS, LDN- Clinical Educator
Jason Barker
ND- Clinical Educator
Emaline Brown
ND- Clinical Educator
Dana Filatova
DCN, CNS, LDN- Clinical Educator
Jessy Dhanjal
ND- Clinical Educator
Nour Amri
MS, LDN, CNS, CKNS- Clinical Educator
