Free Testosterone (Free T)
Quick answer
What is Free Testosterone (Free T)?
Free testosterone is the unbound, biologically active fraction — about 1-2% of total. It's the number that correlates best with symptoms. Calculated free T (Vermeulen formula from total T + SHBG) is the accurate read; direct assays are unreliable.
- Units:
- pmol/L
- Reference range:
- ≥250 pmol/L (calculated, men 25-55)
- Sample:
- Venous blood (serum)
- Category
- Hormones
- Units
- pmol/L
- Reference range
- ≥250 pmol/L (calculated, men 25-55)
What does a high Free Testosterone result mean?
Rare without exogenous testosterone or low SHBG. Anabolic use, severe insulin resistance, or hyperandrogenism.
What does a low Free Testosterone result mean?
Below 180 pmol/L is functionally low. Common drivers: high SHBG, ageing, obesity, secondary hypogonadism, opioids.
Why does Free Testosterone matter?
Free T explains why men with 'normal' total testosterone still feel awful. If you're only seeing total T on your results, you're missing the read that matters.
FAQs
- Why calculate free T instead of measuring it directly?
- Direct free T assays are unreliable at the low end where it matters. Endocrine Society guidance is calculated free T or equilibrium dialysis.
- What raises free testosterone?
- Lowering SHBG (resolving hyperthyroidism, reducing alcohol) or raising total T. Treating the upstream driver, not the number itself.
References
- [1]Testosterone Therapy in Men with Hypogonadism: Endocrine Society Clinical Practice GuidelineEndocrine Society / JCEM (2018)
Want Free Testosterone interpreted in the context of your full panel? Every FORM bloodwork tier covers it, with an MD walking you through the result.
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