Testosterone (Free)

Calculated Free Testosterone estimates the unbound fraction (~2% of total testosterone). More clinically relevant than total testosterone when SHBG is abnormal.

Also known as:

Calculated Free Testosterone (Vermeulen)

fTST

Testosterone (Free) ranges for

Interpret your result

"Normal" lab range for Testosterone (Free) is between 46 and 224 pg/mL for males:

224

According to European Academy of Andrology, Testosterone (Free) should be above 63.45 pg/mL for males:

69.22

According to OptimalDX, Testosterone (Free) should be between 150 and 224 pg/mL for males:

150

224

Optimal range

Optimal range for Testosterone (Free) appears to be between 100 and 224 pg/mL for males:

100

224

300

Why this optimal range?

Preliminary range is based on functional health organizations including but not limited to those listed above.

Why calculated, not measured? Direct immunoassay methods for free testosterone are unreliable due to cross-reactivity with other steroids and dramatic differences in reference ranges between labs — e.g., LabCorp's analog immunoassay produces values ~4× lower than Quest's method, with no way to convert between them. The gold-standard equilibrium dialysis is too complex and costly for routine use.

The Vermeulen calculation, using total testosterone, SHBG, and albumin, is the most robust approximation — largely independent of SHBG, albumin, and T levels — unlike competing formulas whose accuracy degrades at extreme SHBG values.

This page is marked as a work-in-progress.

The optimal range is derived from a limited number of sources and is subject to change.

Your interpretation

For low

For high

Common reasons for high Testosterone (Free):

High calculated free testosterone is seen with androgen excess, most commonly PCOS in women and exogenous testosterone / anabolic steroid use in men.

In women, it is associated with hirsutism, acne, ovulatory dysfunction, and metabolic abnormalities. Less common causes include congenital adrenal hyperplasia, ovarian hyperthecosis, Cushing syndrome, and androgen-secreting ovarian or adrenal tumors.

In men, persistent elevation should prompt review of testosterone use or supplement exposure; rarer endogenous causes include testicular or adrenal androgen-secreting tumors.

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Precision Health Consultant for Longevity Clinics, Biohacker, and Software Engineer

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I am particularly interested in research on biomarkers associated with all-cause mortality and on defining optimal reference ranges.