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Testosterone, Free

The small part of your testosterone that isn't attached to proteins. Results depend heavily on the lab method, so compare only with a range for the same method.

AI-verified against cited sources. Awaiting expert reviewAlso called cFTLOINC 2991-8

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The usual range for Free Testosterone depends on sex. Choose female or male above to see where you stand.

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What it is

Most testosterone in your blood is attached to proteins, mainly SHBG and albumin. Free testosterone is the small part that is not attached, usually about 1 to 4 percent, and it is the part your cells can use most easily. Labs get a free testosterone result in one of three ways: by a physical method such as equilibrium dialysis or ultrafiltration, by calculating it from total testosterone, SHBG and albumin, or by a direct (analog) immunoassay.

Why it matters

Free testosterone can help when total testosterone is close to the edge of the range, or when something changes SHBG, such as obesity, thyroid disease, liver disease or aging. In those cases total testosterone can look normal while free testosterone is low, or the other way around. Methods give very different numbers, so a result only makes sense next to the range for the same method. Guidelines advise against direct analog kits because they are not reliable.

If it’s low

A low result can mean that total testosterone is low, or that a high SHBG is holding more of it tight. Levels fall with age, and in women they are lower after menopause. Direct analog kits also read much lower than other methods, so a low number on one of those kits may not mean much. Guidelines suggest confirming a low result on another early-morning, fasting sample. Many other things can cause a low result, and your clinician can put it in context.

Common causes

  • A method that reads low, such as a direct analog kit, compared with a range for a different method
  • High SHBG, which holds more testosterone tight (older age, estrogen, an overactive thyroid, liver disease, some anti-seizure medicines)
  • Normal aging
  • Menopause, in women
  • Any cause of low total testosterone, including extra body weight, poor sleep, long-lasting illness or some medicines
  • Problems with the testicles or the pituitary gland (less common)

What can help

  • Ask whether to repeat the test on another early-morning, fasting sample
  • Ask which method was used, and whether a dialysis or calculated result is available
  • Talk with your clinician about sleep, weight, alcohol use and medicines, which can all be linked with testosterone levels

If it’s high

A free testosterone above the range for your method can reflect a low SHBG, which leaves a larger share of testosterone free. It can also come from testosterone or steroid use. In women it is often linked to polycystic ovary syndrome (PCOS). Less often it is linked to the adrenal glands, the ovaries or the testicles. The method matters, so a number that looks high on one method can be usual on another. Your clinician can put it in context.

Common causes

  • A test method or lab that reads higher than the range you are comparing with
  • Low SHBG, which leaves a larger share of testosterone free (for example with extra body weight or an underactive thyroid)
  • Testosterone therapy, anabolic steroids, or supplements that raise hormone levels
  • Polycystic ovary syndrome (PCOS) in women
  • Congenital adrenal hyperplasia or other adrenal gland conditions
  • Ovarian or testicular tumors (uncommon)

What can help

  • Share every hormone, steroid and supplement you use with your clinician
  • Ask which method your lab used and whether the range on your report is for that method
  • Ask whether SHBG, total testosterone or other hormones would help put the number in context

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex and age. Choose women or men to see the one that applies.

See Free Testosterone by age and sex, with the U.S. survey numbers where they exist.

EAU 2026 free testosterone threshold (men, calculated)

  • Below the EAU threshold for free testosteronebelow 220 pmol/L
  • At or above the EAU threshold220 and above pmol/L

If this applies to you

Free Testosterone means a little more for some people. Open the one that fits you.

PCOS

The guideline uses free testosterone alongside total testosterone. It can be calculated, including as the free androgen index, or measured by equilibrium dialysis.

Blood tests for PCOS

On testosterone therapy

Free testosterone is the part not bound to proteins. The Endocrine Society prefers measuring it by equilibrium dialysis, or calculating it from total testosterone, SHBG and albumin with an accurate formula.

Blood tests on testosterone therapy

What can affect your result

  • Method: dialysis, ultrafiltration, calculation and direct analog kits give numbers that can differ several-fold
  • SHBG and albumin: a calculated result depends on both, and a higher SHBG lowers the free share
  • Time of day and fasting: levels are highest in the early morning, and guidelines ask for a fasting sample
  • Age and sex: men's levels tend to fall with age (Labcorp's direct-assay ranges are lower in older men), and women's are lower after menopause (ARUP)
  • Pregnancy: calculated free testosterone is not reliable
  • Hormones and medicines: testosterone therapy, steroids, estrogen and birth control change total testosterone and SHBG
  • Body weight and thyroid status, which change SHBG
  • The method changes the number a lot. Equilibrium dialysis, ultrafiltration, a calculation and a direct analog kit can give results several times apart, so compare only with a range for the same method.
  • High-dose biotin (vitamin B7) can interfere with the immunoassays used to measure total testosterone and SHBG. Labcorp asks that biotin be stopped at least 72 hours before the draw. Check with your clinician first.
  • Gross lipemia (a very fatty sample) may give falsely high results on Labcorp's direct free testosterone test.
  • Calculated free testosterone is not reliable in pregnancy, because estradiol takes up some of SHBG's binding sites (Vermeulen 1999).
  • Some SHBG gene variants are missed by immunoassays or bind testosterone differently, which can throw off a calculated result (Hammond 2016).
  • EDTA plasma is not accepted for ARUP's calculated free testosterone tests.

Early morning, roughly 6 to 10 a.m. at ARUP (07:00 to 10:00 in the EAU guideline), with a fasting sample where possible (Endocrine Society, EAU). Free testosterone shifts when total testosterone or SHBG changes. SHBG has a half-life of about a week (Labcorp), so a lasting change can show within a few weeks.

When to talk to a clinician

A free testosterone result alone rarely needs urgent action. Talk with a clinician if it is outside the range for your method and you have symptoms. For men, the European Association of Urology treats a calculated free testosterone of 220 pmol/L (6.4 ng/dL, about 64 pg/mL) as a reliable threshold, and suggests checking free testosterone when a condition that changes SHBG is present. In women, see a clinician for new or quickly worsening facial or body hair, a deepening voice or missed periods.

Questions you could ask

  • Do you have a range for my age, sex and this method?
  • Should I use the same lab and method each time so I can compare results?
  • Which method did my lab use to get this free testosterone?
  • Could my SHBG, a medicine or a hormone treatment explain it?
  • Should we repeat the test or look at other hormones?
  • Was this result from dialysis, a calculation or a direct kit, and is that method reliable for my question?

Questions people ask

Why do different labs give such different free testosterone ranges?

Free testosterone is hard to measure. Labs use equilibrium dialysis, ultrafiltration, a calculation from total testosterone, SHBG and albumin, or a direct analog immunoassay. For adult men, calculated and dialysis ranges run from roughly 47 to 280 pg/mL, while one lab's direct analog range is only about 7 to 27 pg/mL. Compare your result only with a range for the same method.

Is the direct free testosterone test reliable?

Guidelines advise against it. A 1999 study found that these analog kits read only a fraction of the true free level, and the fraction changes with SHBG. The European Association of Urology says direct measurement with these methods should be avoided. If a decision depends on your result, ask whether a dialysis or calculated result is available.

How do I convert free testosterone units?

1 ng/dL equals 10 pg/mL, so 5 ng/dL is 50 pg/mL. To get pmol/L, multiply pg/mL by 3.47. To get nmol/L, divide pmol/L by 1,000. Some labs print pg/mL as ng/L, which is the same number.

How is calculated free testosterone worked out?

Your lab measures total testosterone, SHBG and usually albumin, then uses a binding equation to estimate the free part, often the Vermeulen method. It needs no extra blood. In pregnancy the equation is not reliable, because estradiol takes up some of SHBG's binding sites.

What is the difference between free and bioavailable testosterone?

Free testosterone is the part with no protein attached. Bioavailable testosterone is the free part plus the part loosely attached to albumin, but not the part held by SHBG. Bioavailable testosterone is ordered less often.

Show the science and sources

Units

  • 1 pg/mL = 1 pg/mL
  • 1 pg/mL = 0.1 ng/dL
  • 1 pg/mL = 3.467 pmol/L
  • 1 pg/mL = 0.003467 nmol/L

Open the Free Testosterone unit converter

Is a change real?

Free Testosterone naturally varies about 9.3% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 29% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Desirable Biological Variation Database specifications, 2014 update (Minchinela J, Ricos C, et al.; the 'Ricos database', a compilation of median published CVI/CVG).

For clinicians and researchers

Free testosterone is the unbound fraction (about 1 to 4% of total, depending on method and lab). More than half of total testosterone is bound to SHBG, and most of the rest is weakly bound to albumin (Labcorp). Equilibrium dialysis is the most accurate method for measuring it (EAU 2026), and the 2023 international PCOS guideline accepts free testosterone assessed by calculation, equilibrium dialysis or ammonium sulfate precipitation. Calculated free testosterone uses total testosterone, SHBG and, usually, albumin in a mass-action binding model (Vermeulen 1999). In that study, calculated values were almost identical to dialysis values except in pregnancy, whereas direct analog immunoassay values were only a fraction of them and the fraction varied with SHBG. The EAU 2026 guideline says direct measurement with these methods should be avoided, recommends calculation using SHBG and albumin, and gives 220 pmol/L (6.4 ng/dL) as a reliable threshold, while noting equilibrium dialysis is the most accurate measurement. Calculations assume every SHBG molecule is detected and binds the same way, which fails for some SHBG variants (Hammond 2016). Published intervals therefore depend on the method and lab: for adult men, calculated 47-244 pg/mL (ARUP), dialysis 52-280 (Labcorp), ultrafiltration 50-210 (Labcorp) and direct analog about 7-27 (Labcorp). For adult women, ARUP's calculated (mass-spectrometry-based) 0.6-9.2 pg/mL depending on age and menopause, and dialysis 1.1-6.3 (Labcorp). The Endocrine Society (2018) recommends free testosterone, by equilibrium dialysis or an accurate formula, when total testosterone is near the lower limit of normal or SHBG is altered. The AUA (2018) notes it may help when total testosterone is 230 to 317 ng/dL. Units: 1 ng/dL = 10 pg/mL, and pmol/L = pg/mL x 3.47.

LOINC 2991-8 (primary), 14914-6, 103227-5, 96559-0, 49042-5. Specimen: serum.

Sources

  1. Testosterone, Free (Adult Males or Individuals on Testosterone Hormone Therapy) (test 0070111), ARUP Laboratories
  2. Testosterone, Free (Adult Females, Children, or Individuals on Testosterone-Suppressing Hormone Therapy) (test 0081059), ARUP Laboratories
  3. Testosterone, Free, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences) (test 500726), Labcorp
  4. Testosterone, Free, Equilibrium Ultrafiltration With Total Testosterone, LC/MS-MS (test 070038), Labcorp
  5. Testosterone, Free, Direct (test 144980), Labcorp
  6. Testosterone Levels Test, MedlinePlus (National Library of Medicine)
  7. A critical evaluation of simple methods for the estimation of free testosterone in serum, Journal of Clinical Endocrinology & Metabolism (1999)
  8. Plasma steroid-binding proteins: primary gatekeepers of steroid hormone action, Journal of Endocrinology (2016)
  9. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2018)
  10. Evaluation and Management of Testosterone Deficiency: AUA Guideline, American Urological Association (2018)
  11. EAU Guidelines on Sexual and Reproductive Health: Male Hypogonadism, European Association of Urology (2026)
  12. Recommendations From the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome, Journal of Clinical Endocrinology & Metabolism (2023)
  13. Testosterone (PubChem compound 6013), PubChem (National Library of Medicine)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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