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    47 Testosterone
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    47 Testosterone

    Testosterone: functions, morning reference range in men, causes of low and high levels and how it is measured.

    Testosterone is the main male sex hormone (androgen). In men it is produced mainly by the testes under the control of luteinising hormone (LH) from the pituitary; in women smaller amounts are made by the ovaries and adrenal glands. It is needed for development of the male reproductive organs, sperm production, muscle and bone mass, body hair, red blood cell production, libido and mood. Adult men have blood levels roughly 7–8 times higher than women, and their daily production is about 20 times higher. Testosterone also has important effects on the cardiovascular system and metabolism.

    HormonesAndrogensReproduction
    Men, morning serumlower limit ≈ 9 nmol/L (≈ 264 ng/dL)
    Conversion1 nmol/L ≈ 28.8 ng/dL
    In this appdaily excretion, µmol/24 h
    Diagnosis of deficiencysymptoms + repeatedly low level
    Morning total testosterone in adult men: below about 9 nanomoles per litre low, above that within or above the reference range; results depend on the assay Total testosterone, men (nmol/L, morning) Low below ≈ 9 9 Reference range ≈ 9–32 32 High above range
    Figure 1. Morning total testosterone in adult men. Hypogonadism is diagnosed only when symptoms are present and low values are confirmed on repeated morning measurements.

    Measurement

    Testosterone is highest in the morning, so blood is taken fasting between about 7 and 10 a.m. and an abnormal result is repeated. Free or bioavailable testosterone is calculated when sex hormone-binding globulin (SHBG) is abnormal (obesity, ageing, liver disease, thyroid disease). This application reports testosterone as daily excretion (µmol/24 h), which reflects total daily production but is not used for diagnosis in current guidelines.

    Clinical significance

    Low testosterone

    Men: testicular failure (Klinefelter syndrome, injury, chemotherapy), pituitary or hypothalamic disease, obesity and type 2 diabetes, opioids and glucocorticoids, chronic illness, ageing. Symptoms: low libido, erectile dysfunction, fatigue, loss of muscle and bone, anaemia, breast enlargement, infertility.

    High testosterone

    Women: polycystic ovary syndrome, congenital adrenal hyperplasia, androgen-secreting tumours; signs include excess hair, acne, irregular periods. Men and women: use of anabolic steroids or testosterone (risks: high haematocrit, infertility, liver and heart effects).

    When to see a doctor

    Persistent low libido, erectile dysfunction, loss of body hair or muscle in men, or new excess hair, deepening voice and irregular periods in women should be assessed by an endocrinologist. Testosterone treatment should only be started after confirmed deficiency.

    References

    1. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744. doi:10.1210/jc.2018-00229

    This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

    Published on 1 May 2024