Laboratory test · Skin, hair and nails
Free testosterone
- Sample: venous blood
- Preparation: morning, fasting; men 7–10 h
Test price
- Sample
- venous blood
- Preparation
- morning, fasting; men 7–10 h
Paymentcash, cards and instalments
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Free testosterone is the small portion of blood testosterone not bound to proteins and therefore able to act directly on tissues. A doctor requests it when total testosterone does not give the true picture, most often due to altered SHBG: in men with suspected testosterone deficiency and women with signs of excess male hormones.
Who the test is for
- men with reduced sex drive, erectile dysfunction, fatigue or muscle loss when total testosterone is borderline;
- men with conditions affecting SHBG, such as obesity, diabetes, older age or liver or thyroid disease;
- women with increased hair growth, acne or hair loss;
- women with irregular cycles;
- women with suspected polycystic ovary syndrome (PCOS).
What free testosterone is and what it shows
Most blood testosterone is bound to proteins: tightly to SHBG (sex hormone-binding globulin), and more loosely to albumin. Only around 2 % is free. Tissues can use free testosterone and testosterone loosely bound to albumin, while SHBG-bound testosterone remains in the blood.
Test total testosterone measures all testosterone together, so it depends on SHBG. SHBG is often reduced in obesity, insulin resistance and type 2 diabetes and an underactive thyroid, and raised in older age, an overactive thyroid, liver disease and with some medicines. Total testosterone can then be misleading, while free testosterone better reflects the amount actually available to tissues.
Free androgen index (FAI)
The free androgen index (FAI) is a simple ratio of total testosterone to SHBG. It is used mainly in women, for example when assessing polycystic ovary syndrome. It is unreliable in men, particularly with low SHBG, so free testosterone is assessed instead.
Save with a panel
Test Free testosterone is also included in these panels.
Preparation and sample
Blood is taken from a vein. Preparation is the same as for total testosterone. Come in the morning fasting, after 8 to 12 hours without food (water is permitted). Men give blood between 7 and 10, not during acute illness or after a sleepless night. In women, cycle day is not crucial unless a doctor specifies otherwise. If you take testosterone, other hormonal preparations or biotin (for example hair and nail supplements), mention this during collection.
How to interpret the result
The reference interval depends on sex, age and method and is printed on your report. A doctor interprets it alongside total testosterone, SHBG, symptoms and age.
Low free testosterone in men
Low free testosterone with symptoms supports a diagnosis of testosterone deficiency (hypogonadism), particularly when total testosterone is borderline. One result is insufficient: a doctor usually requests a repeat fasting morning measurement and investigates the cause using LH, FSH and prolactin. Free testosterone is more often reduced by obesity and type 2 diabetes, older age, severe chronic diseases and some medicines.
High free testosterone
In women the most common cause is polycystic ovary syndrome. With insulin resistance and obesity SHBG is low, so free testosterone may be raised despite normal total testosterone. Less often, adrenal dysfunction is responsible, and very rarely an ovarian or adrenal tumour, suggested by very high levels and rapidly developing symptoms. In men, high free testosterone most often results from testosterone or anabolic steroid use.
How to arrange testing
You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Come in the morning fasting; men should come between 7 and 10. Prices for all tests and panels are in the service price list. Total testosterone, SHBG and albumin, important for interpreting free testosterone, are measured together in the Free testosterone panel.
Frequently asked questions
What is the difference between free and total testosterone?
Total testosterone includes all blood testosterone, bound and free. Free testosterone is the small unbound portion that acts on tissues. Total testosterone is usually sufficient initially, while free testosterone is requested when total levels are borderline or SHBG is altered.
What does low free testosterone with normal total testosterone mean?
Most often SHBG is raised, so a large portion is tightly bound; this is more common in older age and some liver or thyroid diseases. A doctor assesses whether it explains symptoms alongside repeat measurement and other findings.
What is the free androgen index (FAI)?
It is the ratio of total testosterone to SHBG, helping assess excess male hormones in women. It is unreliable in men, so free testosterone is assessed instead.
Should free testosterone be measured in women?
For women with signs of excess male hormones, a doctor often requests free testosterone or FAI because total testosterone can be normal with low SHBG. A broader investigation of suspected PCOS is covered by the PCOS panel.