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Answer · biomarkers

Total testosterone vs free testosterone — which one matters?

Short answer

Both matter. Total testosterone measures everything in circulation; free testosterone measures the unbound fraction available to tissues. SHBG drives the relationship — which is why all three are read together rather than any one in isolation.

Reviewed by Dr. Laura PurdyMay 29, 2026

Full answer

Both matter, and neither is sufficient alone. Total testosterone measures all circulating testosterone — bound (to SHBG and albumin) plus unbound (free). Free testosterone measures the small unbound fraction that is biologically active at androgen receptors. SHBG (sex hormone-binding globulin) is the variable that connects them: higher SHBG ties up more testosterone, so a man with high SHBG can have a 'normal' total testosterone but a low free fraction (and low-T symptoms); a man with low SHBG can have a normal total but a higher free fraction (and a metabolically unfavorable context). For this reason provider review almost always reads total testosterone, free testosterone, and SHBG together — and treats discrepancies between them as clinically informative, not as noise.

Educational. Not a substitute for individualized provider review.

References & sources
  • Total testosterone — Primary source · oMeds
  • Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29

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Related answers

What is SHBG?
SHBG (sex hormone–binding globulin) is the liver-produced protein that binds testosterone and estradiol in circulation. It determines how much hormone is bioavailable. Reading total testosterone without SHBG is reading half the picture — two men with identical totals can have very different free testosterone depending on SHBG.
What is free testosterone?
Free testosterone is the fraction of circulating testosterone that is not bound to SHBG and is biologically available to tissues. It is frequently the more clinically meaningful number, because two men with identical total testosterone can have very different free testosterone depending on SHBG.
What is optimal testosterone?
Conventional reference ranges for total testosterone run roughly 300–1,000 ng/dL. Provider-reviewed optimization targets the upper-mid range — typically 600–900 ng/dL in symptomatic men — read against free testosterone, SHBG, estradiol, and the patient's own baseline rather than a population average.
Does TRT lower SHBG?
Yes — typically. Exogenous testosterone usually lowers SHBG, which increases the free fraction of circulating testosterone. The magnitude varies by modality and dose. Low SHBG can change how the patient feels and how the dose should be read.
Can low SHBG cause symptoms?
Low SHBG itself is not a symptom — it is a signal. It typically points to insulin resistance, obesity, hypothyroidism, or exogenous androgen exposure, and it changes how total testosterone should be interpreted (more free, but often in a metabolically unfavorable context).
Primary source
Total testosterone