Testosterone is the primary sex hormone in men, produced mainly by the testes, but it is also present in women at lower levels, produced by the ovaries and adrenal glands. It plays a role in muscle mass, bone density, fat distribution, mood, energy and sexual health in both sexes.
A testosterone blood test measures the level circulating in your bloodstream. Results can be reported as total testosterone, free testosterone, or both — and understanding the difference matters for interpreting your results correctly.
This guide explains the test, what normal ranges look like for men and women, and what high or low results mean.
Total vs free testosterone
About 98% of testosterone in the blood is bound to proteins — mainly sex hormone-binding globulin (SHBG) and albumin. Only the remaining 2% — 'free testosterone' — is immediately biologically active.
Total testosterone measures both bound and free. It's the standard first test. If total testosterone is borderline or doesn't match symptoms, doctors often also test free testosterone and SHBG to get a fuller picture.
Blood should ideally be drawn in the morning, when testosterone is at its daily peak (7–10 a.m.), and on two separate occasions to confirm a low result.
What are normal testosterone levels?
| Group | Normal range (approximate) |
|---|---|
| Adult men | 10–35 nmol/L (300–1000 ng/dL) |
| Adult women | 0.5–2.6 nmol/L (14–76 ng/dL) |
| Men over 65 | Often lower; many labs adjust reference ranges |
Low testosterone in men (hypogonadism)
Testosterone naturally declines with age — roughly 1–2% per year after 30. When levels fall below the normal range and produce symptoms, this is called hypogonadism. Common symptoms include fatigue, reduced libido, difficulty concentrating, low mood, reduced muscle mass and increased body fat.
Causes include problems with the testes themselves (primary hypogonadism), pituitary or hypothalamic disorders (secondary hypogonadism), obesity, chronic illness, sleep apnoea and — importantly — anabolic steroid use, which suppresses the body's own production.
High testosterone in women
Elevated testosterone in women is most commonly caused by polycystic ovary syndrome (PCOS). Symptoms include irregular periods, acne, excess facial or body hair (hirsutism) and difficulty conceiving. Less commonly, elevated testosterone results from adrenal gland disorders or ovarian tumours.
Low testosterone in women
Women also need adequate testosterone for energy, bone strength and sexual health. Levels naturally fall after menopause. Low testosterone in women is not yet well defined clinically, but is associated with fatigue, reduced libido and low mood. Testing is most useful when comparing against previous personal baseline values.
Tracking testosterone over time
If you are being treated for a testosterone condition — testosterone replacement therapy, PCOS management or monitoring of a pituitary disorder — your doctor will check levels regularly. Keeping a trend of results in Looms helps you and your doctor see whether treatment is hitting the right target. Prolactin is often ordered alongside testosterone; our guide to prolactin levels explains the relationship between these two hormones.