Free Testosterone

Free testosterone is the amount of testosterone in your blood that is not bound to proteins and is therefore directly available to your body cells. For men, the reference value lies roughly between 156 and 813 pmol/L, depending on age; for women, between 1 and 41 pmol/L. A value outside this range may indicate a disturbed hormonal balance that can cause symptoms such as fatigue, loss of libido, or infertility.

Reference values

• Women (20–50 years): 1 – 41 pmol/L
• Women (from 50 years): 1 – 27 pmol/L
• Men (20–50 years): 210 – 813 pmol/L
• Men (50–80 years): 185 – 750 pmol/L
• Men (from 80 years): 156 – 686 pmol/L

What is Free Testosterone?

Free testosterone is the biologically active fraction of testosterone: the part that you cells can actually use. Testosterone plays a role in muscle mass, bone density, libido, mood, and energy levels. Both men and women produce testosterone, but in vastly different amounts.

Most of the testosterone in your blood is bound to proteins, particularly to SHBG (sex hormone-binding globulin) and, to a lesser extent, to albumin. Only the unbound portion, free testosterone, can bind to receptors in your cells and exert an effect there. That makes this measurement more relevant than the total testosterone value when you want to know how active the hormone actually is.

How does it work in the body?

Testosterone is produced in the testicles in men and in the ovaries and adrenal glands in women. Once in the bloodstream, most testosterone binds to SHBG. SHBG acts as a type of transport protein that holds the hormone and thereby temporarily inactivates it. The higher the SHBG level in your blood, the less free testosterone remains.

In practice, free testosterone is often calculated using a formula that takes into account the SHBG value in addition to total testosterone, and sometimes albumin. This calculated value provides a good estimate of what is actually available to your cells. A direct laboratory measurement is also possible, but the calculated method is the most common in clinical practice.

Why is Free Testosterone tested?

This measurement provides insight when total testosterone alone does not tell the whole story. This is the case when someone has symptoms that may indicate a hormonal problem, but where the total testosterone value appears normal. If SHBG is significantly elevated, total testosterone may fall within the reference range while there is still insufficient active testosterone available.

Common reasons for having free testosterone tested are:

• Symptoms of erectile dysfunction or reduced libido in men
• Infertility investigations in men or women
• Suspicion of a hormonal imbalance, such as in polycystic ovary syndrome (PCOS) in women
• Fatigue, mood problems, or muscle loss without a clear cause
• Monitoring during hormone therapy use

Symptoms associated with an abnormal value

Both values ​​that are too low and those that are too high can cause noticeable symptoms. The exact symptoms that occur depend on the sex and the degree of deviation.

With a value that is too low:

• Reduced libido or sexual interest
• Fatigue and lack of energy
• Decrease in muscle mass or strength
• Mood swings or feelings of depression
• Reduced bone density in the long term
• Possibly reduced fertility in men due to lower sperm production

With a value that is too high:

• Acne or oilier skin
• Increased body hair
• Mood swings or irritability
• Poorer sleep or restless nights

What influences the value?

Various factors can influence the outcome of a free testosterone test. It is useful to know these before your blood draw.

Time of draw: Testosterone follows a diurnal rhythm. The value is highest early in the morning and decreases throughout the day. Blood for testosterone is preferably drawn between 7:00 and 10:00 AM for the most reliable measurement.

Age: In men, testosterone production gradually decreases with age. This is normal and affects the reference values, which differ by age group.

Body weight and lifestyle: Being overweight can lower SHBG levels, which affects the calculation of free testosterone. Intensive exercise, sleep deprivation, and chronic stress can also temporarily affect testosterone levels.

Medication: Hormone preparations, contraceptives, corticosteroids, and certain medications for the thyroid or blood pressure can alter the SHBG value and, indirectly, the free testosterone value. Always discuss your medication use with your doctor when requesting this test.

Fasting: For a free testosterone measurement, a fasting blood draw is usually not strictly necessary, but always follow the instructions of the laboratory performing the sample collection.