Hormones · Blood

Free testosterone

The small, active part of testosterone that is not bound to protein; calculated from total testosterone, SHBG and albumin.

At a glance

Measured in blood
In 10 test panels
No special preparation

Explanation

Free testosterone: what is measured?

About 98 percent of the testosterone in the blood is bound to the proteins SHBG and albumin; only the remaining 1 to 3 percent is free and can act in the tissues. This value is not measured directly but calculated from total testosterone, SHBG and albumin. It gives a better picture of the active hormone if SHBG is abnormal, for example with overweight, liver disease, older age or pill use.

What can it detect?

Testosterone deficiency in men in whom total testosterone is hard to interpret because of an abnormal SHBG (borderline range, overweight, older age)
Too much active male hormone in women with PCOS or excess hair growth, even if total testosterone is still normal

Result

What does the result mean?

Free testosterone too high

In women, a raised free testosterone fits PCOS or, more rarely, an adrenal disorder; symptoms are acne, excess hair growth, hair loss on the scalp and an irregular cycle. In men, a high value comes mainly from testosterone use or anabolic steroids, or from a low SHBG with overweight or insulin resistance. Because the value is calculated, a low SHBG also raises free testosterone even when nothing is wrong.

Free testosterone too low

In men, a low free testosterone, together with a low or low-normal total testosterone and symptoms, points to testosterone deficiency. A low value without symptoms or from a single measurement has little meaning: the calculation takes over all the fluctuations and measurement errors of total testosterone and SHBG. Illness, malnutrition, lack of sleep and medicines such as opioids and corticosteroids temporarily lower the value. In women, a low free testosterone is not a recognized diagnosis.

After an abnormal result

The GP assesses the value together with total testosterone and SHBG and repeats the measurement in the morning after a few weeks. With a repeatedly low value and symptoms, tests for the cause follow (LH, FSH, prolactin) and usually referral to an internist-endocrinologist or urologist.

Reliability

How reliable is the test?

Free testosterone is a calculated value and inherits the uncertainty of total testosterone and SHBG; the cut-off value differs by laboratory and by formula. The guidance of the Dutch Society for Endocrinology (NVE) advises calculating it if total testosterone is in the borderline range (around 8 to 12 nmol/L) or if SHBG is abnormal, and always with the laboratory's own cut-off value. A direct measurement of free testosterone is not reliable; that is why the value is calculated.

What can affect the result?

The same timing requirement as total testosterone: sample collection in the morning before 11 o'clock, preferably fasting; in the afternoon the value is lower.
Formula and cut-off value differ by laboratory; the 'free androgen index' (FAI) overestimates free testosterone when SHBG is low and is therefore less useful (NVE guidance).
Anything that changes SHBG (overweight, liver disease, thyroid disorder, the pill, anabolic steroids, older age) changes the calculated value.
In women, the measured amounts are so small that the calculation is inaccurate; the result can only be interpreted together with symptoms and other hormones.

Who it is for

Who is the test useful for?

Useful for

Useful as an addition to total testosterone in men with symptoms of a deficiency and a total value in the borderline range, and in men with overweight, liver disease or at older ages, in whom SHBG is often abnormal. In women with excess hair growth, acne or an irregular cycle, together with SHBG it gives a better picture than total testosterone alone. Without symptoms, a calculated free testosterone has no value.

How common is it?

Testosterone deficiency with symptoms is estimated to occur in 2 to 6 in 100 men over 40, more often at older ages and with overweight. Especially with overweight, total testosterone is often low while free testosterone is still normal; that is why this calculation has the most value there.

European population studies (EMAS) as cited in Dutch guidelines; NVE guidance on the effect of overweight

Drawbacks and risks

Because the cut-off value differs by laboratory and formula, a 'too low' value from an online table is easily misinterpreted and seen as a reason to use testosterone.

Get tested

Free testosterone: test panels

Free testosterone is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.

Blood draw
Bodybuilder Test
Panel for strength and muscle development; hormones, liver, and muscles.
€ 134,00
Blood draw
Free Testosterone
Available testosterone; calculated using total testosterone, SHBG, and albumin.
€ 71,00
Blood draw
InsideTracker
InsideTracker Blood Analysis: analyze 48 biomarkers for complete health optimization and personalized recommendations.
€ 335,00
Blood draw
Hormones Male
Total testosterone, free testosterone, SHBG, creatinine, and eGFR. For men with hypogonadism, low libido, or during strength training.
€ 125,00
Blood draw
Hormone Recovery (After Steroids)
Testosterone, free testosterone, SHBG, LH, FSH, estradiol, TSH, liver function, and lipid profile. For recovery after anabolic steroid use.
€ 325,00
Blood draw
Endurance Sports
Complete blood count, iron status (ferritin, transferrin), kidney function, liver function, testosterone, and hs-CRP. For athletes and endurance sport participants.
€ 203,00
Blood draw
Expanded: Testosterone Replacement Therapy (TRT)
Testosterone, LH, FSH, estradiol, prolactin, blood values, complete liver function, kidney function, and lipid profile.
€ 235,00
Blood draw
Supplemental: Testosterone Replacement Therapy (TRT)
Complete hormonal analysis with testosterone, DHEA-S, thyroid, blood count, liver function, kidney function, lipids, glucose, HbA1c, insulin, hs-CRP, vitamin D and ferritin.
€ 335,00
Blood draw
Whoop (Advanced Labs)
Comprehensive blood analysis with biomarkers that integrates directly with your WHOOP wearable for optimal performance and recovery.
€ 385,00

How reliable is the test?

Free testosterone