Free testosterone is the small fraction of testosterone that circulates unbound to proteins, leaving it able to enter cells and act on tissues directly. Because it reflects the biologically active hormone rather than the total pool, it often tracks your symptoms more closely when binding proteins run unusually high or low.
| Group | Typical range | Units |
|---|---|---|
| Adult men | 8.7 to 25.1 | pg/mL |
| Adult women | 0.0 to 4.2 | pg/mL |
Ranges vary by lab, age, and assay method, so compare to the range on your own lab report.
What free testosterone measures
Free testosterone represents the roughly 1 to 4 percent of circulating testosterone that is not attached to sex hormone binding globulin (SHBG) or albumin. This unbound portion is the fraction available to bind androgen receptors and drive effects on libido, muscle, bone, and red blood cell production. Most labs do not measure it directly but calculate it from total testosterone and SHBG, while reference labs may use equilibrium dialysis for greater accuracy.
What high or low levels mean
Low free testosterone can produce classic symptoms of low testosterone, including reduced libido, fatigue, low mood, and loss of muscle mass, even when your total testosterone reads normal. This pattern often points to elevated SHBG, which is common with aging, hyperthyroidism, and some liver conditions, since more binding leaves less hormone in the active free form. High free testosterone in women may signal polycystic ovary syndrome (PCOS) or another source of androgen excess, sometimes alongside acne, irregular cycles, or excess hair growth. Because the value is usually calculated from total testosterone and SHBG, an unusual result should be confirmed with a repeat early-morning sample and read against your symptoms. If levels stay abnormal, follow up with a clinician for LH, FSH, and further evaluation.
Free testosterone FAQ
What is a normal free testosterone level?
In adult men, direct free testosterone typically falls near 8.7 to 25.1 pg/mL and declines gradually with age, while adult women sit much lower at roughly 0.0 to 4.2 pg/mL. Your exact range depends on the assay and reporting lab.
Why is my free testosterone low when total testosterone is normal?
High SHBG is the usual reason. When more testosterone binds to this protein, less stays free and active, so symptoms can appear despite a normal total. Aging, thyroid disease, and certain liver patterns raise SHBG.
How is free testosterone measured?
Most labs calculate it from total testosterone and SHBG using validated equations. Reference laboratories may instead use equilibrium dialysis, considered the most accurate method, which physically separates the unbound fraction before measurement. Read alongside total testosterone, bioavailable testosterone, and sex hormone binding globulin for a fuller picture of your androgen status.
References
- Labcorp, Testosterone, Free, Direct, age-specific reference intervals.
- Jasuja R, et al. Reference intervals for free testosterone in adult men measured using a standardized equilibrium dialysis procedure.
