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.

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.

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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