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 low Testosterone (Free):

Low free testosterone with inappropriately normal total testosterone suggests reduced bioavailable testosterone, most often seen with high SHBG. In men, this pattern may still be consistent with androgen deficiency if symptoms are present.

Low free testosterone with low total testosterone suggests true androgen deficiency / hypogonadism.

In men, low free testosterone is associated with late-onset hypogonadism, chronic opioid use, type 2 diabetes, metabolic syndrome, reduced muscle mass, poorer physical function, and worse self-rated health.

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

Please send me relevant research and feedback.

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