Primary male sex hormone (also measured on some women’s panels); linked to libido, muscle, mood, and cycle health.
What it is
Testosterone is an androgen produced mainly in the testes in men and in smaller amounts in the ovaries and adrenal glands in women. Laboratories report total testosterone in nanomoles per litre (nmol/L) with sex-specific reference intervals. “Total” means bound plus unbound hormone; much is carried on SHBG and albumin, so free or bioavailable estimates are sometimes calculated when SHBG is abnormal.
In men, morning samples (typically before 10:00) are preferred because of diurnal variation. In women, timing relative to the menstrual cycle and any hormonal contraception matters for interpretation.
Immunoassays and mass spectrometry differ in accuracy at low concentrations (important in women and children). Morning male samples reduce diurnal noise. Free testosterone is calculated or measured when SHBG is extreme.
Why it matters
In men, low total testosterone with symptoms (reduced libido, erectile change, loss of morning erections, fatigue, low mood, reduced muscle) may prompt a work-up for hypogonadism, but obesity, sleep apnoea, opioids, high prolactin, and illness can all suppress levels. A repeat morning test and SHBG are often needed before any treatment discussion.
In women, raised testosterone can feature in polycystic ovary syndrome (PCOS) pathways alongside irregular cycles and androgen symptoms, but PCOS is a clinical diagnosis, not a single hormone number. Low values in women are interpreted differently and often less actionable in isolation.
Do not start testosterone therapy from a direct-to-consumer result. UK endocrine guidance emphasises proper diagnosis, contraindications, and monitoring.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Testosterone supports muscle protein synthesis, bone density, red-cell production, libido, and aspects of mood and motivation via androgen receptors in many tissues. In men, the hypothalamic–pituitary–gonadal axis regulates production; disruption at any level alters blood levels.
Excess can drive acne, hair changes, voice deepening, menstrual disturbance, and, at pharmacological doses, higher haematocrit and other risks. Physiology explains why haematocrit and PSA are monitored when men are treated under specialist care.
For athletes
Athletes track testosterone when exploring low energy availability, overreaching, or libido/recovery changes, especially in heavy endurance blocks. Absolute levels vary widely; symptoms and free testosterone / SHBG often matter more than chasing a “high-normal” total.
Anabolic steroid use and some SARMs suppress natural production and distort panels: disclose use to clinicians for safe interpretation. Female athletes with oligomenorrhoea need a broader endocrine and relative-energy-deficiency review, not testosterone alone. Training does not replace medical assessment of hypogonadal symptoms.
Related tests
Showing 6 of 8 panels that include Total testosterone.
For fertility planning when you want AMH with key reproductive and thyroid markers in one private panel. AMH does not predict natural conception chances.
