Written by
Dr. Mei-yin Gruber
MBBS
Normal range
Male: 198–619 pmol/L Female: 3–33 pmol/L
When Testosterone Levels Fall Short
Low testosterone in men
Testosterone deficiency in men can affect several aspects of health. Sexual symptoms, including reduced libido, fewer spontaneous or morning erections and erectile dysfunction, are among the more specific symptoms. Other possible features include fatigue, reduced muscle mass and strength, low mood and reduced bone density.
However, these symptoms are not unique to testosterone deficiency and can have many other causes. A diagnosis of hypogonadism therefore requires symptoms alongside appropriate biochemical testing rather than being based on symptoms or a single testosterone result alone.
Testosterone in women
Women also produce testosterone, although circulating concentrations are considerably lower than in men. Testosterone and other androgens contribute to normal female physiology, including sexual function.
Unlike in men, however, there is no well-defined blood testosterone concentration that can be used to diagnose a generalised “testosterone deficiency” syndrome in otherwise healthy women. Symptoms such as fatigue, low mood or difficulty building muscle are non-specific and should not automatically be attributed to low testosterone.
Free testosterone measurements can instead be particularly useful when investigating androgen excess in women. High androgen levels may be associated with symptoms such as increased facial or body hair, acne, scalp hair thinning and irregular menstrual cycles. Polycystic ovary syndrome (PCOS) is the most common cause of androgen excess in women.
Why Your Free and Total Testosterone Levels May Differ
Because SHBG binds testosterone strongly, changes in SHBG can affect how much testosterone is circulating freely.
If your SHBG level is high, a greater proportion of your testosterone will be bound. You may therefore have a total testosterone result within the normal range while your free testosterone is relatively low.
The opposite can also happen. If your SHBG level is low, your total testosterone may appear low while your free testosterone remains within the reference range.
This is why free testosterone can provide additional information when total testosterone does not fit with the clinical picture or when SHBG levels are outside the normal range.
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The Testosterone–Health Connection
Muscle and bone health: Testosterone supports the development and maintenance of muscle mass and contributes to bone health. Prolonged testosterone deficiency in men can therefore be associated with reduced muscle mass and lower bone mineral density.
Sexual and reproductive health: Testosterone plays an important role in libido and sexual function. In men, adequate testosterone production is also important for normal reproductive function.
Red blood cell production: Testosterone stimulates red blood cell production. Testosterone deficiency in men can therefore sometimes be associated with anaemia.
Rather than free testosterone having completely different functions from total testosterone, these measurements provide different ways of assessing the same hormone. You can read more about the wider functions of testosterone in our testosterone guide.
Understanding Your Results
Free testosterone levels differ considerably between men and women and also tend to change with age.
Men's normal ranges:
Ages 18-49: 198–619 pmol/L
Ages 50+: 163–473 pmol/L
Women's normal ranges:
Ages 18-49: 3–33 pmol/L
Ages 50+: 1–20 pmol/L
Reference ranges can vary between laboratories depending on the testing method and calculation used. Your result should therefore always be interpreted using the reference range provided by the laboratory that performed your test.
Free testosterone is often calculated using your total testosterone, SHBG and albumin levels rather than measured directly. Looking at these results together can help explain why your free testosterone may be high or low.
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The Takeaway
Free testosterone represents the small proportion of testosterone in your blood that is not bound to SHBG or albumin. Because SHBG levels vary between individuals, your free testosterone can sometimes provide useful additional information that isn't apparent from total testosterone alone.
Free testosterone is particularly useful when SHBG levels are unusually high or low, or when your total testosterone result does not fit with your symptoms or other test results. It should therefore be interpreted alongside total testosterone, SHBG and your wider clinical picture rather than considered in isolation.
References
British Society for Sexual Medicine. (2020). Testosterone deficiency in men: diagnosis and management. BSSM Guidelines.
National Institute for Health and Care Excellence. (2019). Testosterone replacement therapy in men. NICE Clinical Guideline.
Royal College of Physicians. (2021). Hormone testing in androgen deficiency. RCP Practice Guidelines.
Society for Endocrinology and Association of Clinical Biochemistry and Laboratory Medicine. (2023). Standardising the biochemical confirmation of adult male hypogonadism: a joint position statement. Endocrine Connections.
