Testosterone: The Complete Guide
Testosterone shapes everything from energy and mood to muscle, bone strength and sex drive. It's the main male sex hormone, though women produce it too. This guide explains what testosterone does, the signs your levels might be low, and how a testosterone test can show you where you stand.
What is testosterone?
Testosterone is the primary male sex hormone. In men, it's made mainly in the testicles. Women produce smaller amounts in the ovaries and adrenal glands, where it helps keep hormones in balance.
It's behind many of the changes that happen during puberty, like a deeper voice and body hair, but its job doesn't stop there. Throughout adult life, testosterone supports your sex drive and fertility, keeps muscle and bone strong, and influences mood and energy. When levels drift too high or too low, you can feel the difference.
What does testosterone do in the body?
Testosterone plays a role in several everyday functions:
- Sex drive and sexual function
- Building and maintaining muscle
- Keeping bones strong and dense
- Supporting red blood cell production
- Mood, motivation and concentration
- How your body stores fat
Symptoms of low testosterone
Low testosterone can be easy to miss, because the signs can creep in slowly and overlap with everyday tiredness or stress.
In men
Common signs of low testosterone in men may include:
- A drop in sex drive or difficulty with erections
- Ongoing fatigue or low energy
- Loss of muscle strength
- More body fat, particularly around the middle
- Low mood, irritability or trouble concentrating
These symptoms don't always mean testosterone is to blame; poor sleep, stress and getting older can cause the same feelings.
With that said, low testosterone is often associated with low mood, and Bluecrest data shows a third of men who check their mental health screen positive for symptoms of depression or anxiety. A test is the only way to know whether your hormones are part of the picture.
In women
Women can experience low testosterone too, most often after the menopause. Signs may include low libido, low energy, reduced strength and mood changes. Because these symptoms are easy to attribute to other causes, they're frequently overlooked.
What causes low testosterone?
Testosterone levels fall naturally with age, dropping by around 1% a year from your late 30s onwards. That's a normal part of getting older, but several other factors can lower your levels:
- Poor sleep and ongoing stress
- Carrying excess weight and related metabolic issues
- Medical causes, including hypogonadism (where the testicles, pituitary gland or hypothalamus don't work as they should)
- Certain medications
There's a two-way link between testosterone and metabolic health, as low testosterone is often connected with type 2 diabetes. It's a reminder that hormones rarely act in isolation. Bluecrest data shows 1 in 8 men are pre-diabetic or diabetic, and many have no idea.
What is a testosterone test?
A testosterone test is a simple blood test that measures the level of the hormone in your blood. Because testosterone is highest in the early part of the day, the sample needs to be taken in the morning, before 11am, for an accurate result. A sample taken in the afternoon can read misleadingly low.
The four markers a good testosterone test measures
People usually attribute a testosterone test to a single number. In reality, a clear view of your hormonal health looks at four things:
- Total testosterone: all the testosterone in your blood.
- Free testosterone: the small fraction that isn't bound to proteins and is available for your body to use.
- SHBG (sex hormone binding globulin): a protein that binds to testosterone and controls how much is free.
- Albumin: another protein that carries testosterone around the body.
Only around 2-3% of your testosterone is "free" and active. Two men with the same total testosterone can have very different amounts available to their tissues, depending on their SHBG and albumin. Our Male Testosterone Profile measures all four, so you get a clearer read than a single number can give.
Understanding your testosterone levels (nmol/L)
In the UK, testosterone is measured in nanomoles per litre (nmol/L). Ranges vary between laboratories and shift with age, which is why the same result can be read differently from one provider to the next. As a general guide:
| Total testosterone (nmol/L) | What it generally suggests |
|---|---|
| Roughly 8.7–29 | Typical adult male reference range |
| Below 12 (with symptoms) | May be considered low; worth investigating |
| Below 8 | Clearly low; warrants further assessment |
These figures are a guide, not a diagnosis. NHS reference ranges vary between laboratories; some trusts use around 6–27 nmol/L, for example, while the British Society for Sexual Medicine flags levels below 12 nmol/L as potentially low where symptoms are present.
Every Bluecrest result comes with a red, amber or green flag, so you can see at a glance whether a reading needs attention.
When should you consider a testosterone test?
Consider a test if you:
- Have symptoms of low testosterone, such as low energy, low libido or reduced strength
- Are a man over 40 keeping an eye on your health
- Want to track changes over time or check the effect of a medication
If you'd rather go through the NHS, your GP can arrange a blood test and, where needed, refer you to a specialist. A private test is an option if you'd prefer to check your levels conveniently, without a wait. You can test on its own or as part of one of our hormone profiles.
How a Bluecrest testosterone test works
Booking a test is straightforward:
- Choose your test. Book the testosterone test on its own, or add it to a full body health check.
- Pick a time and place. Choose a morning appointment at a venue near you. We run health checks from over 350 venues across the UK and Ireland.
- Attend your appointment. A health specialist takes your blood sample. The whole visit takes around 20–30 minutes.
- Get your results. View them through the My Wellness app with clear red, amber or green flags, backed by access to our 24/7 GP helpline.
Find a clinic near you and book online today.
Take control of your testosterone
Some of the biggest influences on your testosterone are within your control. Regular exercise, good sleep and a healthy weight all support healthy levels. A test tells you where you're starting from, so any changes you make are guided by real data.
Frequently asked questions
Do I need to fast for a testosterone test?
Some providers recommend fasting, others don't. If you book with Bluecrest, we'll send full preparation instructions when you book, so you know exactly what to do. Drink plenty of water beforehand, and let us know about any medications or supplements you're taking.
What time of day should a testosterone test be done?
In the morning, before 11am. Testosterone levels are highest early in the day, so a morning sample gives the most accurate result.
What's a normal testosterone level for a man?
The typical adult male range is roughly 8.6–29 nmol/L, though this varies by lab and age. Levels below 12 nmol/L, alongside symptoms, may be considered low and worth investigating.
Can women have a testosterone test?
Yes. Women have lower levels of testosterone, and abnormal results can point to conditions such as polycystic ovary syndrome. A test is suitable for anyone concerned their levels may be off.
Can I take a testosterone test at home?
You can, but an at-home kit won't always give the fullest picture. Testing at one of our venues, with a sample taken and processed by a leading UK laboratory, gives you more complete and reliable results.
Anna Jones
Chief Nursing Officer, BluecrestGraham Jones
Medical Writer
