Fertility & hormones
Testosterone blood test
A testosterone blood test measures the main sex hormone in the blood, important for libido, energy, mood, muscle and bone in men, and relevant to women too. It is usually measured as total testosterone, with free testosterone and SHBG (the protein that binds testosterone) added to work out how much is actually active.
- What it measures
- The sex hormone testosterone (total, and often free)
- Sample
- Venous blood sample
- Fasting
- Morning sample preferred
- Also known as
- total testosterone, free testosterone, SHBG
- Included in 57 Health tests
- 8 panels, from £60
What does a high testosterone level mean?
In men, a high testosterone level is uncommon and is usually looked into rather than dismissed. It can come from testosterone or anabolic steroid use, and less often from problems in the testicles, adrenal glands or pituitary. In women, a raised level is more common and is often linked to polycystic ovary syndrome (PCOS), which can cause irregular periods, acne or excess hair.
A single high reading is interpreted with SHBG, the free testosterone and other hormones, because what matters is the active fraction and the overall pattern, not one number in isolation.
What does a low testosterone level mean?
In men, a low testosterone can cause low libido, tiredness, low mood, poor concentration, reduced muscle and erectile difficulties. Because levels are highest in the morning and dip later in the day, a genuinely low result is confirmed on a second morning sample before it is acted on. Common contributors include ageing, carrying extra weight, poor sleep, stress and some long-term conditions and medicines.
Testosterone is carried by SHBG, so a high SHBG can leave less free (active) testosterone even when the total looks normal, which is why free testosterone is often calculated. In women, testosterone falls gradually with age and around the menopause, and low levels may play a part in low libido.
When to consider a testosterone test
- Low libido or erectile difficulties
- Persistent tiredness, low mood or brain fog
- Loss of muscle strength or stamina
- Monitoring testosterone replacement therapy (TRT)
- Irregular periods, acne or excess hair in women (PCOS)
- Investigating fertility concerns
Frequently asked questions
This page is general information about a blood marker and is not medical advice or a diagnosis. A testosterone test screens and gives context; results are interpreted by a clinician alongside your symptoms, history and other markers. Always follow the guidance on your own report.