Testosterone (T) is an important androgen, belonging to the steroid hormone family. It is generally caused by Leydig cells in the testes in men, but in women, it is secreted a little by the ovaries and adrenal glands. Testosterone has the effect of refreshing people, fighting osteoporosis, and maintaining muscle strength and quality.
Testosterone plays multiple roles in the human body, especially in the development and maintenance of gender characteristics:
1. Sexual development: During adolescence, testosterone promotes the development of male secondary sexual characteristics, such as thicker voice, increased body hair, and muscular development.
2. Reproductive function: Testosterone is essential for sperm production and affects sexual desire and sexual function.
3. Bone Health: Testosterone helps maintain bone density and strength.
4. Muscle development: Testosterone promotes protein synthesis and enhances muscle mass and strength.
5. Red blood cell production: Testosterone stimulates the bone marrow to produce red blood cells and improves the oxygen-carrying capacity of the blood. 
Tips:
In addition, testosterone affects many body systems and functions, including blood production, calcium balance, bone mineralization, lipid metabolism, glucose metabolism, and prostate growth. It is the main male sex hormone and anabolic hormone, and it has an important impact on health for both men and women.
Testosterone examination and normal values
Testosterone levels are usually checked with a blood test. Your doctor may recommend this test to evaluate reproductive health, pubertal development, sexual dysfunction in men, or hirsutism and other hormone-related symptoms in women.
Normal value range
The standard range for normal testosterone levels varies depending on the measurement method and reference standard used by the laboratory, and also varies with age and gender. The following are general reference ranges (usually expressed in nanomoles per liter (nmol/L) or nanograms per deciliter (ng/dL)):
Adult male
Total Testosterone: 8.4 – 28.4 nmol/L or 240 – 800 ng/dL
Free testosterone: 0.17 – 0.7 nmol/L or 5 – 20 pg/mL
Adult women
Total Testosterone: 0.52 – 2.43 nmol/L or 15 – 70 ng/dL
Free testosterone: 0.03- 0.39 nmol/L or 1 – 11 pg/mL
Children
Boys: < 0.7 nmol/L or < 20 ng/dL
Girls: < 0.7 nmol/L or < 20 ng/dL
Pregnant women
Pregnant women: 2.7～5.3nmol/L
PS: The normal value of testosterone will change according to different periods. The data is for reference, and the specific judgment needs to be made by a doctor.
Notes
Testosterone levels fluctuate throughout the day, usually peaking in the morning, so to get more accurate results, blood tests are often scheduled in the morning. 
Dangers of high testosterone
High testosterone is extremely dangerous to both men and women. The most important effect is on bone growth. If the human body secretes too much testosterone, it will cause certain harm to the body. The details are as follows:
1. Prostate problems
Chronically high levels of testosterone may increase the risk of prostate hyperplasia and prostate cancer.
2. Reduced sperm count
Excessive testosterone harms the stable process of sperm formation, causing a decrease in sperm quality and quantity.
3. Obvious masculine characteristics
Women may experience masculine characteristics such as a thickened voice, increased facial and body hair (hirsutism), hair loss, acne, and an enlarged clitoris.
4. Premature development
May cause precocious puberty, the early onset of puberty, which may affect ultimate potential for height.
5. Female infertility
Excessive testosterone can also lead to endocrine disorders or polycystic ovary syndrome in women, which can easily affect women\’s stable pregnancy and subsequently lead to infertility.
