• Testosterone is the main male sex hormone. Females also have it but in smaller amounts.
• Changes in testosterone levels can impact on your health in many ways depending on your sex and age.
• Two types of testosterone are measured. These are termed bound and free.
• A total testosterone test measures both bound and free forms of testosterone.
• Total testosterone is usually ordered along with tests for other related hormones such as luteinizing hormone (LH), follicle stimulating hormone (FSH) and gonadotropin-releasing hormone (GnRH).
• Changes in testosterone levels can suggest either the hypothalamus, the pituitary gland or the testicles or ovaries aren’t working as they should be.

Testosterone is the main male sex hormone. Females also have it but in smaller amounts. It is one of several androgens (male sex hormones) in both men and women. Testosterone causes the changes that occur in boys during puberty. It helps the development of masculine features including the growth of the penis and testicles, facial and public hair, increased muscle and bone strength and the deepening of the voice. It is made in the testicles and is needed for sperm production and the sex drive.

In females, testosterone is made in the ovaries (where eggs are stored) and the adrenal glands, which sit just on top of the kidneys. It is responsible for sexual function, bone health, and muscle mass. The amount of testosterone produced in females is mostly converted to oestradiol, which is the main female sex hormone.

In both males and females, testosterone plays a wider role in overall health, influencing mood, energy levels and sex drive, and affecting many organs including the heart, circulation and brain function.

How testosterone levels are controlled

The amount of testosterone made and released by the testicles (testes) or ovaries is controlled by a feedback system of hormones and glands that ensures levels are stable.

Hormones are chemical messengers that are made by your glands and travel in your bloodstream to control the actions of specific cells in your tissues or organs. When they reach their target, they attach to a cell’s receptors, stimulating a response.

• When testosterone levels in the blood are low, a part of the brain called the hypothalamus, signals to the pituitary gland which sits just underneath the brain.
• It does this by releasing gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gland to release luteinizing hormone (LH).
• LH then stimulates the production and release of testosterone in the testicles or the ovaries.
• FSH works alongside LH in reproductive health: in males, it regulates sperm production, and in females, it aids in the maturation of ovarian follicles.
• As testosterone in the blood increases, production of GnRH slows down, which helps keep testosterone levels stable.

Changes to testosterone levels may occur if the hypothalamus, the pituitary gland or the testicles or ovaries aren’t working as they should.

How testosterone levels vary

Testosterone has important effects at different stages of life including:

• Fetal development: At about the seventh week of pregnancy, the baby’s testicles produce testosterone which starts the development of the male reproductive organs.
• Puberty in male children: Testosterone starts many of the changes seen in pubescent males, such as increasing height, body and pubic hair growth, enlargement of the penis, testicles and prostate gland and increasing sex drive.
• Adulthood in males: Testosterone is needed to produce sperm, make new red blood cells, build bone and muscle strength, maintain sex drive and general well-being.
• Adulthood in females: Testosterone affects sex drive with low levels leading to low sex drive, especially in post-menopausal women.

What tests measure testosterone?

Once testosterone is made, it is released into the bloodstream. Most of the testosterone in your blood attaches to two proteins: sex hormone binding globulin (SHBG) and albumin. This helps prevent tissues from using testosterone straight away and keeps levels stable.

Some testosterone is called free testosterone, which means it is not attached to proteins, but it is in circulation. Free testosterone that is not bound to protein is available to act on your tissues.

Both bound and free testosterone are measured in a single test called total testosterone. This is the test that is most often ordered.

The levels of testosterone in your blood are highest in the morning and fall during the day.

Abnormalities in the level of SHBG can affect the amount of testosterone that is available to the tissues so a total testosterone may not provide an accurate measurement. In this case, your doctor may request both a total testosterone and an SHBG level as part of your investigations. For more on this see SHBG.

It is also possible to measure free testosterone directly, and this test may occasionally be requested when measuring SHGB and total testosterone levels does not give a clear picture.

Changes to the normal levels of testosterone in your body can lead to various conditions.

Boys

The testosterone test is used along with LH and FSH tests to investigate delayed or early puberty. Normally, puberty begins at about the age of 10 but delays may be due to low testosterone production by the testicles – called primary hypogonadism - or if the pituitary does not produce enough LH – called secondary hypogonadism.

Men

Infertility, decreased sex drive or erectile dysfunction can all be due to a low testosterone level and your doctor will likely request testosterone as well as FSH and LH. Testosterone levels decline with age, and abnormally high or low levels can lead to various health issues, such as decreased muscle mass, fatigue, mood changes or fertility problems.

Women

Testosterone may be measured to investigate irregular or no menstrual periods (amenorrhoea), difficulty in getting pregnant, or masculine features such as facial and body hair, male pattern baldness and low voice.

In both men and women testosterone may be measured to investigate a possible tumour of the testicles, ovary or adrenal gland.

Sample

Blood

Any preparation?

None

Reading your test report

Your results will generally be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Testosterone measurements

There is a very wide range of testosterone levels, and your test results may vary depending on your age, sex and health history. They may vary depending on the assay used by the laboratory doing the test. It is important to compare your results to the reference or healthy range quoted by the laboratory that performed your tests.

Reference Intervals

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people
• When compared against them your results may be flagged high or low if they sit outside the range.
• Reference ranges may vary between different age groups.
• Reference intervals may vary between labs so only those results that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. Your doctor needs to take your medical history to help interpret your result.

• Alcoholism and liver disease in males can decrease testosterone levels.
• Drugs, including steroids, can also decrease testosterone levels.
• Treatment for prostate cancer includes androgens which reduce testosterone levels.

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods, medications or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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