Testosterone
Primary male sex hormone for muscle building, libido, and energy
Also known as
Definition
Testosterone is the primary androgen, produced in the testes (men), ovaries, and adrenal glands (women). It is responsible for muscle building, bone density, libido, mood, energy metabolism, and erythropoiesis. Total testosterone encompasses free testosterone (~2–3%), albumin-bound (~38%), and SHBG-bound (~60%). Only free and albumin-bound testosterone is biologically active (= bioavailable testosterone).
| Parameter | Value |
|---|---|
| Unit | nmol/l (ng/dl) |
| Reference Range | Men: 9.9–27.8 nmol/l (286–800 ng/dl) | Women: 0.29–1.67 nmol/l (8–48 ng/dl) |
Agree on your personal target range with your doctor.
Conversion: 1 nmol/l = 28.8 ng/dl. US labs use ng/dl (men: 270–1,070 ng/dl).
↓ What a low value means
Hypogonadism (men: < 9.9 nmol/l; women: < 0.29 nmol/l) can be primary (testicular/ovarian failure) or secondary (pituitary/hypothalamic). Symptoms: loss of libido, erectile dysfunction, muscle wasting, bone density loss, anemia, depression, fatigue, increased body fat. Testosterone in men declines ~1–2% per year from age 30.
↑ What a high value means
Elevated values in women (> 1.67 nmol/l) can indicate PCOS, congenital adrenal hyperplasia, or androgen-producing tumors. In men: anabolic steroids, testosterone therapy, or rarely a Leydig cell tumor. Symptoms in women: hirsutism, acne, menstrual irregularities, clitoral hypertrophy.
✓ What can influence this value
The testosterone value is influenced by age (in men it declines slowly from age 30), sleep (testosterone is produced mainly at night, and sleep deprivation can lower the value), body fat percentage and excess weight, resistance training, stress, and zinc supply. Conditions of the testes, pituitary, or hypothalamus, as well as anabolic steroids and testosterone therapy, change the value markedly. The time of day of the blood draw and differences between laboratories also affect the result. The assessment is made by the treating doctor.
When to test
Blood is drawn in the morning between 7 and 10 am (circadian peak), fasting. Reasons for testing are symptoms such as loss of libido, fatigue, muscle loss, or infertility. SHBG is often measured as well, as SHBG changes strongly influence the free fraction; free testosterone can then be calculated or measured directly.
Frequently asked questions
What is the difference between total testosterone and free testosterone? +
Total testosterone measures all fractions: free (2–3%), albumin-bound (~38%), and SHBG-bound (~60%). Only free and albumin-bound testosterone is biologically active. High SHBG (from liver cirrhosis, hyperthyroidism, estrogen, aging) can produce low free testosterone and hypogonadism symptoms despite normal total testosterone.
How much does testosterone decline with age? +
In men, total testosterone declines ~1–2% per year from age 30 (EMAS study). Free testosterone declines faster (~2–3%/year) as SHBG rises with age. By age 70, the average man has 30–40% less testosterone than at 30. This decline is variable and highly dependent on lifestyle.
Can women also have testosterone deficiency? +
Yes. Women produce testosterone in the ovaries and adrenal glands; it is important for libido, muscle strength, and bone density. After menopause or oophorectomy, testosterone declines markedly. In women, symptoms such as loss of libido, fatigue, and muscle weakness can also be linked to testosterone deficiency.
What role does the testosterone value play in the question of replacement therapy? +
The Endocrine Society guideline requires repeatedly low morning values together with clinical symptoms for hypogonadism in men; a low value alone is not enough, and neither are symptoms alone. Testosterone replacement therapy suppresses sperm production. Your doctor decides whether and how to treat.
Testosterone
Sources
- Bhasin S et al. (2018) Testosterone Therapy in Men with Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab.
- Wu FCW et al. (2010) Identification of late-onset hypogonadism in middle-aged and elderly men (EMAS). N Engl J Med.
- Travison TG et al. (2007) A population-level decline in serum testosterone levels in American men. J Clin Endocrinol Metab.
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.