What is Testosterone?

Testosterone is the male sex hormone (androgen) produced in the testicles.  A small amount is also produced in the adrenal glands and in the female ovaries.

How testosterone work?

Production starts at the onset of puberty and continues throughout a man’s life, but the levels start to slowly decline from the fifties onwards, finally fading to nothing in the eighties as the man passes through the andropause (the male equivalent of the menopause). It is responsible for the development of male characteristics (eg. facial hair, penis enlargement at puberty) in a man, and is produced in response to hormonal signals from the pituitary gland, which lies under the brain.

Testosterone levels:

The total amount of testosterone present in the blood can be measured. The normal levels are:-

Male 12 to 34 nmol/L
Female 0.4 to 3.6 nmol/L
Before puberty 0.4 to 0.7 nmol/L

Low levels occur with male hypogonadism (under active testes), panhypopituitarism (under active pituitary gland under the brain), male menopause (andropause), delayed puberty, Addison disease and other causes of sterility.

High levels may be found with a virilising adrenal tumour (tumour of adrenal glands on kidneys that produces testosterone) and the Stein-Leventhal syndrome. In women there are higher levels during pregnancy and with oestrogen therapy.

A second blood test that can be performed is to measure the free testosterone. This measures the amount of the hormone in the blood that is not attached to a protein and is circulating freely. This free testosterone test is a less accurate test than testosterone. It is normally used to test for signs of female hirsutism (excess facial hair and other male characteristics) and male sexual dysfunction. The normal results are:-

Female 16 to 40 years 3 to 12 pmol/L
Female 40+ years 2 to 10 pmol/L
Male 16 to 40 years 60 to 130 pmol/L
Male 41 to 70 years 40 to 100 pmol/L
Male 70+ years 30 to 90 pmol/L

The interpretation of high and low results is the same as for total testosterone.

Testosterone may also be used as a medication to treat sex hormone deficiency in males, male infertility, male osteoporosis and Klinefelter syndrome. In combination with oestrogen it is used in the female menopause and after removal of the ovaries in women. It may also be used to increase libido in women. It is available as capsules, patches, cream, implants or injections.

It should not be used in pregnancy, breastfeeding or children, or if suffering from prostate or breast cancer. Use testosterone with caution in heart disease, kidney disease, migraine, diabetes, epilepsy and high blood pressure. Side effects may include unwanted penile erections, retention of fluid, nausea and oily faeces. It may interact with cyclosporin and hypoglycaemic medications (used to treat diabetes).

Long-term inappropriate use may cause infertility, shrinking of testes, increased muscle bulk, high blood pressure, heart failure and increased risk of heart attack. It does not cause addiction or dependence, but testosterone is sometimes used illegally and inappropriately by athletes and body builders, with potentially serious consequences.


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