Free Testosterone
Free testosterone is the unbound, biologically active fraction of total testosterone (about 2-3%). Only free testosterone can enter cells, bind to androgen receptors, and exert biological effects. It can be directly measured (equilibrium dialysis is gold standard) or calculated from total testosterone, SHBG, and albumin using the Vermeulen equation.
Why it matters: Free testosterone is the most clinically relevant testosterone measure. A man with normal total testosterone but high SHBG may have low free testosterone and symptomatic hypogonadism. Conversely, low total testosterone with low SHBG (common in obesity) may have adequate free testosterone. Free testosterone resolves discordance between total testosterone and symptoms.
May increase with:
May decrease with:
What is Free Testosterone?
Free testosterone is the unbound, biologically active fraction of total testosterone (about 2-3%). Only free testosterone can enter cells, bind to androgen receptors, and exert biological effects. It can be directly measured (equilibrium dialysis is gold standard) or calculated from total testosterone, SHBG, and albumin using the Vermeulen equation.
What might a high or low Free Testosterone mean?
Free testosterone is the most clinically relevant testosterone measure. A man with normal total testosterone but high SHBG may have low free testosterone and symptomatic hypogonadism. Conversely, low total testosterone with low SHBG (common in obesity) may have adequate free testosterone. Free testosterone resolves discordance between total testosterone and symptoms.
What is the typical reference range for Free Testosterone?
The general-population reference range shown here is 0.05 – 0.21 ng/mL. Reference ranges describe the general population and are not a personal target — discuss your results with your physician.
What can affect Free Testosterone?
It may be higher with: Same factors as total testosterone, Lowering SHBG (weight loss in obese, treating hyperthyroidism), Resistance training, Testosterone replacement therapy, Boron supplementation (modest reduction of SHBG). It may be lower with: Elevated SHBG (aging, liver disease, hyperthyroidism, oral estrogen), Aging, Obesity (complex — lowers total T but also lowers SHBG), Chronic illness.
Track your Free Testosterone over time
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