lab metric
FT (male-only)
Table of contents
Description
Free Testosterone is the small fraction of testosterone that is unbound (“free”) in the bloodstream and therefore most available to enter tissues and activate androgen receptors. In men, it can be more closely related to symptoms than total testosterone—especially when SHBG is unusually high or low.
Why it matters
Testosterone influences libido, mood, energy, muscle mass, bone density, and red blood cell production. Two people can have the same total testosterone but very different free testosterone depending on SHBG; that’s why free (or bioavailable) testosterone is often used to clarify borderline cases.
How to interpret it well
Timing: levels are usually highest in the morning; clinicians often prefer early-morning testing.
Repeat testing: a single low value is often rechecked under typical sleep/stress conditions.
Context labs: interpret alongside total testosterone, SHBG, LH/FSH, and symptoms.
Common drivers of low free testosterone
Higher SHBG (aging, hyperthyroidism, some liver patterns), obesity/insulin resistance, poor sleep, chronic illness, and certain medications can all lower free testosterone.
Educational only, not medical advice. Hormone labs and symptoms should be reviewed with a clinician, and treatment decisions require individualized evaluation and monitoring.
Frequently Asked Questions
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