What is testosterone?
Testosterone is essential for normal sexual development and function in both men and women, and testing testosterone levels is sometimes required if you’re showing signs of deficiency.
Testosterone is an androgen and is the dominant male sex hormone. In males, testosterone is involved in secondary sexual characteristics such as body hair growth, muscle development, penis enlargement and a deepened voice. The majority of testosterone is produced in the testes, with the adrenal glands also producing a small amount.
For women, it is the adrenals, along with the ovaries, that produce testosterone.
Luteinizing hormone (LH) controls testosterone production. When testosterone levels drop, the body produces LH to stimulate testosterone production; when testosterone increases, LH levels reduce.
Testosterone levels in both sexes start to naturally decline from our mid-thirties – a process called the andropause – and this can affect general health and wellbeing.
ADAM (androgen deficiency of the aging male) describes the reduced quality of life – including low libido, erectile dysfunction and fatigue – that affects around 10 per cent of men by the age of 70 due to low testosterone levels.
For women, a reduction in testosterone can start to impact libido and mood in our 40s.
Testing testosterone levels
Screening questionnaires are available for men who suspect they have low testosterone levels. If a score indicates possible problems, then blood testing testosterone levels may be the next step.
Testing is not just for older men. It can help diagnose conditions such as erectile dysfunction, infertility, testicular failure (from trauma or infection) and other conditions associated with low testosterone levels.
The test can also assess high levels of testosterone, which may indicate testicular tumors or a benign prostatic hypertrophy/hyperplasia (BPH) – a condition often associated with aging and one that often causes urination problems.
A doctor may also recommend a testosterone test for boys who appear to be commencing puberty too early.
Unfortunately, there are no screening questionnaires available for women; however, if a woman has unexplained persistent tiredness, low libido or a decreased feeling of wellbeing, testing testosterone levels may be worthwhile. The test can also be used for a number of other diagnoses, including infertility, hirsutism (excessive hair growth) and adrenal or ovarian tumors. Higher than normal levels of testosterone in women can indicate polycystic ovary syndrome (PCOS).
What it involves
Testing testosterone levels involves having a small blood sample taken from the arm and sent for analysis. The time of testing may take into account daily variations in testosterone -levels are usually highest in the early morning and lowest in the late afternoon or evening.
Total testosterone is usually measured when testing testosterone levels. Much of the testosterone in our body is bound to sex hormone binding globulin (SHBG), a protein that carries testosterone in the blood.
The test might also measure free testosterone, which accounts for between one and four per cent of total testosterone in the blood. This might occur where the total testosterone test is unsuitable, such as if SHBG levels are abnormal.
Testosterone levels are generally measured in units of either nanograms per deciliter (ng/dL) or nanomoles per liter (nmol/L). Although ranges can vary between labs, common result ranges are:
- 300-1000 ng/dL or 10.41-34.70 nmol/L for men
- 15-70 ng/dL or 0.52-2.43 nmol/L for women
Other hormones, such as follicle stimulating hormone (FSH) or LH, may also be tested at the same time as testosterone.
Issues affecting test results
Heavy alcohol consumption and liver disease can affect testosterone test results.
Hormone treatments (such as estrogen) can lead to decreased testosterone levels, while drugs such as barbiturates and other hormones (e.g. growth hormone) can cause elevated levels of testosterone. Exercise also increases testosterone levels.
- Slow Ageing book, Kate Marie and Dr Merlin Thomas
- Bonita Morrow Cavanaugh (2003). Nurse’s Manual of Laboratory and Diagnostic Tests. Fourth Edition. F.A. Davis Company. Philadelphia. Pg 184–185
- Testosterone: http://labtestsonline.org/understanding/analytes/testosterone/tab/faq
- Testosterone: http://www.nlm.nih.gov/medlineplus/ency/article/003707.htm