What the free testosterone test shows
Testosterone does not travel through the blood alone. About 98% of it rides on carrier proteins — held tightly by sex hormone-binding globulin (SHBG), which keeps it out of action, or loosely by albumin — leaving only about 2% completely unbound. That unbound slice is free testosterone; with the albumin-bound fraction it forms the “bioavailable” hormone tissues use, as StatPearls describes.
A total testosterone test adds up everything, free plus bound, and is usually the right first test. Free testosterone matters when the carrier proteins misbehave: because SHBG shifts with age, weight, thyroid status and estrogen, total testosterone can read “normal” while the usable fraction is low. MedlinePlus notes it is the less common test — used in men for low-testosterone symptoms and in women for signs of hormone excess.
Free testosterone normal range
Free testosterone is reported in pg/mL, sometimes in ng/dL (1 ng/dL = 10 pg/mL) or as a percentage of total; SI labs use pmol/L (1 pg/mL ≈ 3.47 pmol/L). Ranges vary more between labs than for almost any other hormone: the accurate methods are equilibrium dialysis or a calculated free testosterone. These orientation values from Mayo Clinic Laboratories decline with age in men:
| Group | Free testosterone, pg/mL (≈ pmol/L) |
|---|---|
| Men, 20–30 | ~50–210 (≈ 175–730) |
| Men, 40–50 | ~45–170 (≈ 155–590) |
| Men, 60+ | ~35–140 (≈ 120–485) |
| Women, adult | ~1–11 (≈ 3–40) |
| Children / teenagers | use the lab’s age-specific range |
Male levels fall about 1–2% a year from age 30–40, and female levels drop after menopause. Ranges depend on the lab, sex, age and assay — read against your own report’s range.
Why free testosterone is low
Low free testosterone matters most in men, where it defines male hypogonadism: low libido, erectile difficulty, fatigue, low mood and loss of muscle. Causes split into two groups, which is why it is paired with LH and FSH:
- Primary (testicular) — LH and FSH run high: Klinefelter syndrome, past mumps orchitis, testicular injury, chemotherapy or radiation.
- Secondary (pituitary or hypothalamic) — LH and FSH are low or normal: pituitary tumors, high prolactin, iron overload from hemochromatosis (high ferritin), opioids, and — commonest of all — obesity, type 2 diabetes and metabolic syndrome, which also lower SHBG.
Because excess weight lowers SHBG, a man’s total testosterone can read low even when his free testosterone is still normal — which is exactly why free or calculated free testosterone is the better guide when SHBG is off. The Endocrine Society advises confirming any low value on a second morning, fasting sample before diagnosing hypogonadism. The one urgent pattern — new hypogonadism with headaches or visual changes — points to a pituitary mass and needs prompt imaging.
Why free testosterone is high
High free testosterone is mainly a question in women, where it is the signature of androgen excess: unwanted hair growth (hirsutism), acne, scalp-hair thinning and irregular periods. Roughly by frequency:
- Polycystic ovary syndrome (PCOS) — by far the commonest cause. Insulin resistance lowers SHBG, so free testosterone can be raised even when total testosterone looks normal, per MedlinePlus. Worked up with LH, glucose and AMH.
- Non-classic congenital adrenal hyperplasia — screened with 17-OH-progesterone.
- Adrenal source — a high DHEAS points to the adrenal gland, not the ovary.
- Exogenous androgens — anabolic steroids or testosterone therapy, which suppress LH and FSH.
In men, it is usually from testosterone or steroid use rather than disease. The urgent pattern is rapidly worsening virilization in a woman — deepening voice, male-pattern balding or clitoral enlargement over weeks to months — a possible androgen-secreting ovarian or adrenal tumor that needs prompt evaluation.
What to test alongside
Free testosterone is almost never read on its own:
- Total testosterone — the anchor free testosterone refines.
- SHBG — sets how much testosterone stays free.
- LH and FSH — separate gonadal from pituitary causes.
- Prolactin — high levels suppress testosterone.
- Estradiol — testosterone converts to estradiol; relevant in gynecomastia.
- DHEAS and 17-OH-progesterone — trace female androgen excess to the adrenal gland.
- AMH — often raised in PCOS.
- TSH — thyroid disease shifts SHBG and mimics symptoms.
- Glucose and HbA1c — insulin resistance underlies both low SHBG and PCOS.
- Ferritin — high iron stores can cause pituitary hypogonadism.
What to do about an abnormal result
- Don’t self-treat. Testosterone bought online can shrink the testes, cause infertility, thicken the blood and is dangerous in undiagnosed prostate disease; anti-androgen decisions in women are equally specialist.
- Repeat it correctly. Testosterone peaks in the morning and swings day to day, so an abnormal result is confirmed on a second fasting sample drawn between 8 and 10 a.m.
- Interpret it with SHBG. Free or calculated free testosterone read with SHBG, LH and FSH tells you far more than any single number.
- For low free testosterone in men: a primary-care doctor or endocrinologist looks for a treatable cause — weight, sleep, diabetes, medication, prolactin — before considering therapy. Our men’s health checkup guide covers the wider panel.
- For high free testosterone in women: a primary-care doctor, gynecologist or endocrinologist evaluates for PCOS and, when features are severe or fast-moving, rules out an adrenal or ovarian tumor.
Mini-FAQ
What is the difference between free and total testosterone?
Total testosterone measures all the hormone in your blood, including the roughly 98% bound to SHBG and albumin. Free testosterone measures only the small unbound fraction your tissues use immediately, so it helps most when SHBG is unusually high or low — as in obesity, diabetes, thyroid or liver disease, aging or estrogen use.
What is a normal free testosterone level?
By one common method it is roughly 50–210 pg/mL in young adult men and about 1–11 pg/mL in adult women, but ranges vary widely between assays and fall with age — read your own lab’s range. Levels peak in the morning.
What does high free testosterone mean in women?
Most often polycystic ovary syndrome, the leading cause of androgen excess, with acne, extra hair growth and irregular periods. Less often it reflects a congenital adrenal enzyme problem or, rarely, an androgen-producing tumor.
What does low free testosterone mean in men?
It signals male hypogonadism — low libido, fatigue, erectile problems and loss of muscle. A repeat morning sample plus LH and FSH shows whether the cause is in the testes or the pituitary.
Can low testosterone be raised naturally?
Losing excess weight, treating diabetes, sleeping well and resistance training can all lift a low level, especially when obesity is the driver. Testosterone therapy is a medical decision made only after low levels are confirmed — not a self-prescription.
