Free Testosterone
The fraction of testosterone not bound to proteins and available to your tissues. Often a better reflection of active hormone than total testosterone.
Typical reference range
| Range | Unit |
|---|---|
| 220–800 (male) | pmol/l |
What Free Testosterone measures
Free testosterone is the small fraction of testosterone that is not bound to proteins in the blood and is therefore available to act on tissues. Most testosterone circulates attached to sex hormone-binding globulin (SHBG) or, more loosely, to albumin, and this bound portion is generally not active. Only the unbound, or free, part is thought to interact directly with cells.
Free testosterone is often estimated or measured when total testosterone and SHBG together give an unclear picture, since SHBG shifts how much testosterone ends up free. When SHBG is unusually high or low, total testosterone alone can be misleading, so the free fraction adds useful context. It applies to people of all sexes, though typical levels differ. A clinician usually reads it alongside total testosterone, SHBG, and symptoms.
What a high Free Testosterone can mean
What a high free testosterone can suggest depends heavily on sex and context, and it is not a diagnosis on its own.
- In women and people assigned female at birth: a raised level can relate to polycystic ovary syndrome (PCOS) or other causes of androgen excess. It is sometimes read alongside features such as acne, unwanted hair growth (hirsutism), or irregular cycles, though these have many possible explanations.
- In men and people assigned male at birth: a high value can reflect exogenous testosterone from supplements or therapy, or a low-SHBG state that leaves more testosterone unbound even when total testosterone is unremarkable.
Timing of the blood draw and the SHBG context both matter, since free testosterone shifts with them. A single elevated reading is best confirmed and interpreted with a clinician who knows your history rather than acted on alone.
What a low Free Testosterone can mean
A low free testosterone, particularly in men and people assigned male at birth, can relate to a range of causes rather than pointing to a single one.
- Hypogonadism, where the testes or the signaling from the brain produce less testosterone.
- Aging, as levels tend to decline gradually over time.
- Obesity, chronic illness, or certain medications, which can each lower the free fraction.
Free testosterone can read low even when total testosterone looks normal, especially if SHBG is high and binds up more of the hormone. Symptoms sometimes reported include low libido, fatigue, or low mood, though these are nonspecific. Because levels vary through the day and between draws, a low result usually calls for repeat morning testing and interpretation within the full clinical picture by a clinician.
Track your Free Testosterone over time in Quanome — it reads your lab reports (PDF or photo) on your device, charts each marker against its range, and an AI coach explains what your trends mean alongside your Apple Health and DNA.