Biomarker Glossary

Testosterone

Testosterone is the primary male sex hormone, also produced in smaller amounts in women. A testosterone blood test measures total and sometimes free testosterone, and is the standard UK test for investigating low libido, fatigue, muscle loss, infertility, mood changes and other symptoms of hormonal imbalance in both men and women.

Also known as: Total Testosterone, T, Serum Testosterone

Testosterone is most informative when read alongside related markers like SHBG and Oestradiol. A single number rarely tells the whole story. If your reading sits outside the typical range, share the full report with your GP or healthcare professional before drawing conclusions.

What is Testosterone?

Testosterone is produced mainly in the testes in men and in smaller amounts by the ovaries and adrenal glands in women. It drives the development of male secondary sex characteristics, supports muscle mass and bone density, and influences mood, libido and energy in both sexes.

Most testosterone in your blood is bound to proteins (mainly sex hormone binding globulin, or SHBG, and albumin) and is biologically inactive. Only a small fraction circulates as free testosterone, which is the active form your tissues can use.

A standard UK testosterone test measures total testosterone. For a fuller picture, free testosterone, SHBG and the free androgen index (FAI) are often tested together.

Why test Testosterone?

Men: to investigate symptoms of low testosterone such as fatigue, low libido, erectile dysfunction, loss of muscle, depression or weight gain.
Men: to monitor testosterone replacement therapy (TRT).
Women: to investigate PCOS, irregular periods, excess facial or body hair, acne or fertility issues.
To screen as part of a broader hormone panel or biohacking review.

Men: to investigate symptoms of low testosterone such as fatigue, low libido, erectile dysfunction, loss of muscle, depression or weight gain.

Testosterone normal range (UK)

Result	What it means
Men 19 to 50 years: 10 to 30 nmol/L	Normal
Men below 10 nmol/L	Low. Symptoms of hypogonadism may be present.
Men above 30 nmol/L	High. May indicate steroid use or rare tumour
Women: 0.5 to 2.4 nmol/L	Normal
Women above 2.5 nmol/L	High. Often seen in PCOS or adrenal disorders

Ranges are based on Society for Endocrinology UK guidance. Testosterone fluctuates daily. Levels are highest in the morning, so always test between 8am and 10am after a 12 hour fast for the most accurate reading.

About these ranges. The ranges above are typical UK clinical lab ranges aligned to NHS and Royal College of Pathologists guidance. Your Chxhealth report will show the specific reference range used by our partner lab, Randox, for each marker. Lab ranges vary slightly between providers and assays. Always interpret your results in the context of the range printed on your own report.

What causes high Testosterone?

In men: anabolic steroid use, testosterone replacement, rare testicular or adrenal tumours.
In women: polycystic ovary syndrome (PCOS) is the most common cause.
In women: congenital adrenal hyperplasia (CAH)
In women: adrenal or ovarian tumour (rare)
Cushing's syndrome
Some medications and supplements

What causes low Testosterone?

Primary hypogonadism: testicular damage from injury, infection, chemotherapy or autoimmunity
Secondary hypogonadism: pituitary or hypothalamic problems
Obesity (fat tissue converts testosterone to oestrogen)
Type 2 diabetes and metabolic syndrome
Chronic stress and poor sleep
Opioid medications and anabolic steroid abuse history
Klinefelter syndrome and other genetic conditions
Normal age related decline (around 1 percent per year from age 30)

Symptoms of high Testosterone

In men: aggression, mood swings, acne, sleep disturbance (often from supplementation)
In women: excess facial or body hair (hirsutism), acne, deepening voice, irregular periods, scalp hair thinning, increased muscle mass

Symptoms of low Testosterone

Low libido (lack of sex drive)
Erectile dysfunction in men
Fatigue and low energy
Loss of muscle mass and strength
Increased body fat, particularly around the abdomen
Mood changes, irritability, low mood or depression
Difficulty concentrating
Poor sleep
Loss of body and facial hair
Decreased bone density and increased fracture risk over time

How is Testosterone tested?

Testosterone is measured from a blood sample, ideally taken between 8am and 10am after a 12 hour fast. Levels naturally peak in the morning and fall through the day.

For accuracy, two morning samples on separate days are recommended if your first result is borderline.

Chxhealth samples are analysed by Randox, a UK laboratory accredited by UKAS. Results return in 3 to 5 working days.

How to support healthy Testosterone levels

Strength train regularly. Compound lifts (squats, deadlifts) raise testosterone acutely and over time.
Lose excess fat. Obesity is one of the biggest reversible causes of low testosterone in men.
Sleep 7 to 9 hours per night. One week of 5 hours sleep lowers testosterone by 10 to 15 percent.
Eat enough protein, healthy fats (olive oil, oily fish, eggs) and zinc rich foods (red meat, oysters, pumpkin seeds).
Reduce alcohol. Heavy drinking suppresses testosterone production.
Manage stress. Chronic cortisol lowers testosterone.

These are general lifestyle suggestions. Chxhealth is an information service. For personal medical advice, please speak to a healthcare professional.

Chxhealth panels that test Testosterone

10 Chxhealth biomarker panels include Testosterone. Each is analysed by Randox, a UK laboratory accredited by UKAS. Reports are delivered in 3 to 5 working days.

Testosterone FAQs

What is a normal testosterone level for men in the UK?

10 to 30 nmol/L is the standard UK reference range for adult men. Below 10 nmol/L is considered low and warrants further investigation, particularly if symptoms of hypogonadism are present.

When should I test testosterone?

Between 8am and 10am after a 12 hour fast. Testosterone naturally peaks in the morning and drops through the day. Afternoon results can be 30 percent lower than morning levels and are not diagnostic.

Should I test total or free testosterone?

Total testosterone is the standard first test. Free testosterone is more useful when SHBG is high or low, when symptoms are present but total is borderline, or when monitoring TRT. Many panels test both.

What is TRT?

Testosterone Replacement Therapy. A treatment prescribed for men with confirmed clinical hypogonadism (low testosterone with symptoms). TRT is a medical treatment and Chxhealth does not prescribe. Speak to a healthcare professional if your results suggest TRT may be appropriate.

Can low testosterone be reversed without TRT?

Often yes, particularly when caused by lifestyle factors such as obesity, poor sleep, heavy alcohol or chronic stress. Many men see testosterone rise significantly within 3 to 6 months of addressing these.

Often tested with Testosterone

The biomarkers below are commonly investigated alongside Testosterone because they reveal connected aspects of the same physiological picture:

SHBG: Calculated free testosterone uses both values, often more useful than total alone.
Oestradiol: Aromatisation of testosterone to oestradiol can affect symptoms.
TSH: Thyroid function influences sex hormones and is worth checking alongside.
Vitamin D: Low vitamin D is sometimes associated with lower testosterone.

Choose the right test for your goal

If you are reading about Testosterone because of a specific health goal, our buying guides walk you through which Chxhealth panels fit:

Sources and further reading

This page is informed by guidance from the NHS, NICE, Royal College of Pathologists and other UK authoritative bodies. For deeper detail or to verify the information, see:

About this page. Last reviewed: 13 May 2026. Next scheduled review: May 2027. This page has not yet been independently reviewed by a clinician. It is written from authoritative UK medical guidance (NHS, NICE, Royal College of Pathologists, peer-reviewed sources) but has not undergone formal clinical sign off.

Important. Chxhealth is a UK information service. We do not diagnose, treat or prescribe. The reference ranges and information on this page are general educational content and should not be used as a substitute for advice from a qualified healthcare professional. For any concerns about your health or results, please speak to your GP or another healthcare professional.