Testosterone

What is being tested?
Testosterone is a steroid hormone (androgen) produced in men by specialised endocrine tissue (the Leydig cells) in the testicles. Its production is stimulated and controlled by luteinising hormone (LH), made in the pituitary gland. Testosterone works through a negative feedback mechanism: if testosterone levels rise, LH falls, while if LH levels rise, testosterone falls. Testosterone levels change during the day, peaking in the early morning (from about 4 to 8 a.m.) and falling to lower levels in the evening (from about 4 to 8 p.m.). Levels also rise after exercise but fall with age. About two thirds of the testosterone circulating in the blood is bound to sex hormone-binding globulin (SHBG) and just under a third is bound to albumin. Only a small percentage (about 1-4%) circulates as free testosterone.
In males, testosterone stimulates the development of secondary sexual characteristics, including enlargement of the penis, growth of body hair, muscle development and a deep voice. It is present in high concentrations in boys during puberty and in adult men, where it regulates sex drive and maintains muscle mass. Testosterone is also produced by the adrenal glands in both men and women and, in small amounts, by the ovaries. In women, testosterone is converted into oestradiol, the main female sex hormone.

How is the sample collected for testing?
A blood sample is taken from a vein in the arm.

1. How is it used?
2. When is it requested?
3. What does the result mean?
4. Is there anything else I should know?

1. How is it used?
Testosterone testing is requested to diagnose different conditions in men, women and boys. These conditions include:

– in boys:

• delayed or early puberty;

– in men:

• erectile dysfunction;
• reduced sex drive;

– in women:

• hirsutism and virilisation;
• ovarian tumours;

– in men and women:

• infertility;
• hypothalamic or pituitary disorders;
• adrenal tumours.

2. When is it requested?
In boys, the test is often requested together with FSH and LH if puberty is delayed or progressing slowly. Although individuals differ, the first hormonal and physical signs of puberty generally appear in boys from the age of 10. Puberty may be delayed if the testicles do not produce enough testosterone or if the pituitary gland does not produce enough LH.
The test may also be requested when a boy is going through puberty early, with obvious secondary sexual characteristics such as enlargement of the penis, muscle development, a change in voice and the appearance of body hair.
In men, the test may be requested when reduced or absent fertility is suspected, or if there is reduced sex drive or erectile dysfunction, which may result from low testosterone levels.
In women, testosterone may be measured if the patient has irregular or absent periods (amenorrhoea), has difficulty having a child, or develops masculine features such as facial or body hair, early baldness or a deep voice.
Testosterone levels may rise because of tumours that can develop in the ovaries or adrenal glands, or because of other conditions such as polycystic ovary syndrome.

3. What does the result mean?
In men, testosterone levels vary widely, and it is normal for them to fall with age.
In men, low testosterone levels may be due to hypothalamic or pituitary disorders, with reduced circulating levels of LH and FSH, or to damage to the testicles, resulting in reduced testosterone production.
Genetic diseases can cause reduced testosterone production in boys (Klinefelter syndrome, Kallmann syndrome and Prader-Willi syndrome) or infertility (as in myotonic dystrophy, a particular form of muscular dystrophy). A low testosterone level may also indicate impaired testosterone production following acquired damage to the testicles, as in alcoholism, physical trauma or viral diseases such as mumps. Testosterone levels may also fall with anabolic steroid abuse.
In women, raised testosterone levels may be a sign of polycystic ovary syndrome, or of an ovarian or adrenal tumour.

4. Is there anything else I should know?
Alcoholism and liver disease can lower testosterone levels in men.
Medicines, including androgens and steroids, can also lower testosterone levels.
Prostate cancer may be treated with hormone therapy that suppresses androgens; testosterone levels therefore fall in men treated with these medicines

1. If my testosterone levels are low, can testosterone supplements help?
2. Why do I need a testosterone test if I am a woman?
3. Is the amount of body hair directly proportional to my testosterone levels?
4. What are free and bioavailable testosterone?

1. If my testosterone levels are low, can testosterone supplements help?
Perhaps. Testosterone levels can be raised with tablets or injections. However, although men with erectile dysfunction may have low testosterone levels, giving the hormone does not improve the symptoms. Testing testosterone together with other hormones can help the doctor understand the cause of the symptoms.

2. Why do I need a testosterone test if I am a woman?
Although in small amounts, the female body also produces testosterone. It is needed for normal body functions and hormonal balance. If the body produces too much testosterone, however, you may have more body hair than normal, irregular or absent periods, or be infertile.
Testing testosterone together with other hormones can help the doctor understand the cause of the symptoms.

3. Is the amount of body hair directly proportional to my testosterone levels?
Some studies have shown a correlation between testosterone levels and the amount of body hair. However, hair growth in response to testosterone differs in different parts of the body. In some men, for example, testosterone causes hair to grow on the abdomen and back, while reducing the growth of scalp hair, leading to baldness.

4. What are free and bioavailable testosterone?
Most circulating testosterone is bound to two proteins, albumin and sex hormone-binding globulin (SHBG). Only a small amount of testosterone (1-4%) is free. Free testosterone is available to the tissues. Testosterone binds only weakly to albumin, so this fraction is also available to the tissues. Free and bioavailable testosterone is therefore a measure of the testosterone available to the tissues.
The amount of bioavailable and free testosterone is affected by SHBG levels. High SHBG levels are due to liver cirrhosis, anticonvulsant therapy, oestrogen therapy and hyperthyroidism. Low levels occur with androgen therapy, nephrotic syndrome, hypothyroidism, polycystic ovary syndrome and obesity. In these cases, free or bioavailable testosterone testing can help with the diagnosis