Free Testosterone Levels: Why Total T Doesn't Tell the Whole Story
Medically reviewed by Medical Advisory Board Last reviewed 2026-09-16
The bioavailable fraction of testosterone that actually drives symptoms
Free testosterone — the 2–3% of total testosterone not bound to proteins — is the biologically active form that enters cells and drives physiological effects. You can have 'normal' total testosterone and still suffer low-T symptoms when free testosterone is low.
Total testosterone includes all testosterone circulating in the blood: free (unbound), albumin-bound (loosely bound), and SHBG-bound (tightly bound). Only free testosterone (1 to 3% of total) and albumin-bound testosterone (~25 to 50%) are bioavailable, meaning they can enter cells and activate androgen receptors. SHBG-bound testosterone (~50 to 70%) is biologically inactive.
This distinction matters enormously in clinical practice. A man with a total testosterone level of 550 ng/dL but an elevated SHBG level of 60 nmol/L may have free testosterone of only 6 ng/dL (60 pg/mL), well within the symptomatic range, even though his total T appears perfectly healthy. SHBG rises with age, hyperthyroidism, liver disease, estrogen exposure, and certain medications, which makes free testosterone an essential companion test.
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| Level | Interpretation |
|---|---|
| >150 pg/mL (15 ng/dL) | Optimal — robust androgenic activity |
| 100–150 pg/mL | Adequate — low risk of symptoms |
| 70–100 pg/mL | Borderline — symptoms may appear |
| 50–70 pg/mL | Low — fatigue, reduced libido, body composition changes likely |
| <50 pg/mL | Deficient — significant symptom burden expected |
Note: Standard lab 'normal' ranges for free T vary by assay method. Direct analog immunoassay (the most common) is less accurate than equilibrium dialysis or calculated free T (Vermeulen equation). Always note which method was used.
Free Testosterone Levels in Women
Free testosterone levels in women are much lower than in men and vary by assay, age, menstrual status, and contraceptive use. Many standard assays are least accurate at the low concentrations seen in women, so results should be interpreted with symptoms and SHBG.
| Life Stage | Typical Free Testosterone* | Pattern |
|---|---|---|
| Reproductive age (20s-30s) | ~1.0-9.0 pg/mL | Highest of the three stages; may run slightly higher around ovulation |
| Perimenopause | ~0.5-6.0 pg/mL | Gradual decline begins years before periods stop |
| Postmenopausal | ~0.5-4.0 pg/mL | Lowest of the three stages as ovarian output drops |
*These are approximate ranges. Female reference ranges vary more by lab and assay than male ranges do. Always check the specific range printed on your own lab report.
Low free testosterone may contribute to low libido, fatigue, and reduced muscle response, especially after menopause or oophorectomy. High free testosterone can point toward PCOS, insulin resistance, adrenal androgen excess, or medication effects. For women, the right target is symptom-guided balance, not male-range optimization.
Why Free Testosterone Can Be Low Despite Normal Total T
Elevated SHBG: Sex hormone binding globulin increases with aging (~1.6% per year after 30), hyperthyroidism, estrogen-containing medications, liver disease (increased hepatic SHBG production), low-calorie diets, and endurance exercise. Higher SHBG means more testosterone is bound and unavailable.
Obesity: Paradoxically, obesity often lowers SHBG but total T drops even more due to aromatase (converting T to estradiol in fat tissue), resulting in low free T and elevated estrogen.
Medications: Opioids, anticonvulsants, and some antidepressants can alter SHBG and free testosterone levels independently of total T.
Free Testosterone High: Causes and Symptoms
Free testosterone can run too high as well as too low, and the causes differ by sex.
In men, the most common cause is exogenous testosterone or anabolic steroid use. Adrenal tumors that secrete androgens are a rare cause. Any condition that lowers SHBG also raises the free fraction, since less testosterone gets bound.
In women, high free testosterone is most often linked to PCOS, insulin resistance, or adrenal androgen excess. Common symptoms include acne, excess hair growth on the face or body, scalp hair thinning, and irregular periods.
What to Test Alongside Free Testosterone
A complete picture requires: Total testosterone (drawn before 10 AM after fasting), Free testosterone (equilibrium dialysis preferred, or calculated), SHBG (the key modifier), Albumin (the other binding protein), Estradiol (sensitive assay — elevated E2 mimics low T symptoms), LH and FSH (distinguish primary from secondary hypogonadism), and Prolactin (elevated levels suppress testosterone production).
How to Get a Free Testosterone Test
Getting an accurate free testosterone result starts with asking for the right test method.
Equilibrium dialysis is the reference-standard method and the most accurate of the three. It's less widely available and takes longer to process. Calculated free testosterone, derived from total testosterone, SHBG, and albumin, is a reasonable practical alternative available at most labs.
Direct immunoassay, often sold under the name "Free Testosterone Direct," is the least accurate of the three. It's particularly unreliable at the low concentrations seen in women.
Free testosterone is usually billed as part of a broader hormone panel. Standalone ordering is also available at most major labs, including Quest Diagnostics and LabCorp.
You can order through a doctor or directly as a consumer. For typical panel pricing and what's included, see our hormone testing guide.
How to test testosterone at home
You don't need a lab appointment to check your own testosterone — a few at-home kits mail you a collection kit and return physician-reviewed results online within days:
Prefer to order direct? The Everlywell Testosterone Test uses a CLIA-certified lab, physician-reviewed results, and prepaid return shipping.
Frequently Asked Questions
What is the difference between free testosterone and total testosterone?
Total testosterone measures all forms — free (unbound), albumin-bound, and SHBG-bound. Free testosterone (1–3% of total) is the unbound fraction that can enter cells and activate androgen receptors. It's the form directly responsible for energy, libido, muscle mass, and mood. You can have normal total T but low free T if SHBG is elevated.
What is free testosterone in women?
Free testosterone in women is the small unbound fraction of testosterone available to tissues. It is biologically active, but women require far lower levels than men. Symptoms, cycle status, SHBG, total testosterone, DHEA-S, and PCOS signs all matter when interpreting a result.
What causes low free testosterone?
The most common cause is elevated SHBG, which increases with aging, hyperthyroidism, liver conditions, and certain medications. Obesity, chronic stress (elevates cortisol, suppresses T production), poor sleep, and excessive alcohol all lower free testosterone. Some men have genuinely low production (primary or secondary hypogonadism).
How do I increase free testosterone naturally?
Strategies include: resistance training (compound movements increase free T 15–20%), maintaining a healthy body fat percentage (15–20% for men), sleeping 7–9 hours (one week of 5-hour sleep reduces T by 10–15%), managing stress (cortisol directly suppresses testosterone), and ensuring adequate zinc (30–45 mg/day), vitamin D (>50 ng/mL), and magnesium intake.
When should I specifically request free or bioavailable testosterone testing?
Ask for free (or bioavailable) testosterone alongside SHBG whenever total testosterone comes back borderline-normal or normal but classic low-T symptoms persist, or when SHBG is known or suspected to be elevated — common with aging, hyperthyroidism, or liver conditions. If a prior workup only measured total T, it's reasonable to request the fuller panel. Equilibrium dialysis or calculated free testosterone (Vermeulen equation) is more accurate than the direct analog immunoassays many labs run by default, so it's worth asking which method your lab uses.
What is "Free Testosterone Direct"?
"Free Testosterone Direct" is the name of a specific direct immunoassay method for measuring free testosterone. Major labs, including Quest Diagnostics and LabCorp, run this test. It measures free testosterone with an antibody-based technique rather than first physically separating bound and unbound hormone. This method is generally considered less accurate than equilibrium dialysis or calculated free testosterone. It's especially unreliable at the low concentrations seen in women. "Free testosterone" has nothing to do with the thyroid "free T3" or "free T4" tests, despite the similar naming. They measure completely different hormones.
Is free testosterone the same as bioavailable testosterone?
No. Bioavailable testosterone is the broader category, made up of free testosterone plus albumin-bound testosterone. Free testosterone alone is only the unbound fraction, roughly 1 to 3% of the total. A bioavailable testosterone test captures both actively usable forms, while a free testosterone test captures only the smallest slice of that pool.
What free testosterone level indicates PCOS?
No single free testosterone number diagnoses PCOS by itself. Elevated free testosterone is one supporting lab finding among several used in a PCOS workup, alongside irregular periods and other signs of androgen excess. Diagnosis typically follows the Rotterdam criteria, which requires meeting two of three broader criteria rather than one lab value alone. See our PCOS and hormones guide for the complete diagnostic workup.
What units is free testosterone measured in?
Free testosterone results can appear in different units depending on the lab. US labs commonly use picograms per milliliter (pg/mL) or nanograms per deciliter (ng/dL). Many labs outside the US report picomoles per liter (pmol/L) instead. To convert pg/mL to pmol/L, multiply by 3.47; to go the other way, divide by 3.47. Reference ranges vary by unit and by assay method. Always compare your result to the range printed on your own lab report, not a number from another source.
Does free testosterone affect hair loss?
Free testosterone contributes to hair loss, but the level alone doesn't decide who loses hair. Scalp follicles vary in how sensitive they are to androgens, and that sensitivity is largely genetic. Two people with the same free testosterone level can have very different hair loss outcomes.
Does free testosterone convert to estrogen?
Yes. Free testosterone converts to estradiol through the same aromatization process as total testosterone, using the enzyme aromatase. This conversion happens mainly in fat tissue, which is one reason body composition affects the balance between testosterone and estrogen.
Does free testosterone affect fertility?
Free testosterone reflects overall androgen status, but it doesn't directly drive sperm production. LH, FSH, and intratesticular testosterone (the concentration inside the testes, much higher than blood levels) matter more directly for fertility. A normal free testosterone reading doesn't rule out a fertility problem, and a low reading doesn't automatically mean infertility.
Does free testosterone fluctuate during the day?
Yes. Free testosterone follows the same diurnal pattern as total testosterone, typically peaking in the morning and declining through the day. This is why standard hormone panels call for a morning blood draw, usually before 10 AM.
What free testosterone level qualifies for TRT?
No major medical organization publishes a single free testosterone cutoff for TRT eligibility. Total testosterone has published thresholds from several organizations, but free testosterone doesn't have an equivalent standard. Clinicians typically use a free testosterone value near or below the bottom of this page's adult reference range as supporting evidence in borderline total testosterone cases, not as a standalone diagnostic threshold. See our TRT guide for the full qualification criteria, including the total testosterone thresholds different organizations use.
Can free testosterone be low with normal FSH and LH?
Yes, free testosterone can be low even when follicle-stimulating hormone (FSH) and luteinizing hormone (LH) fall within normal ranges. Testosterone levels fluctuate from day to day and between individual morning blood draws, so an isolated low reading warrants a repeat test rather than a settled diagnosis. LH release is also pulsatile: because the hormone is secreted in pulses rather than at a constant level, a single draw can miss a pulsatile low and read as normal even when pituitary-testicular signaling is not fully typical. In other cases, this pattern reflects early or mild secondary hypogonadism that hasn't yet produced an abnormal LH or FSH result, or an SHBG abnormality altering the free-testosterone calculation. This pattern is best worked up with a full hormone panel and a repeat morning draw rather than acted on from a single set of numbers. See our guide on the causes of low testosterone for how primary and secondary hypogonadism are distinguished.
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