If your energy has quietly drained away, your sex drive is not what it was, you are losing strength in the gym despite the same effort, and your mood and motivation feel flat, it is easy to put it all down to age or stress. Sometimes that is exactly what it is. But this same cluster of symptoms is also the classic picture of low testosterone, and unlike “getting older”, low testosterone is something you can actually measure and, where appropriate, treat.
The only way to know is a blood test, done properly. A single afternoon reading is not enough, and a “normal” result without the right supporting markers can be misleading. This guide explains what low testosterone actually feels like, what causes it, and what a proper testosterone blood test involves. At WMG Health, our private blood testing service on Harley Street, London, appointments are same-day and every result is reviewed by a GMC-registered doctor.
What low testosterone actually feels like
Testosterone does far more than drive libido, so a genuine deficiency tends to show up across several areas at once rather than as a single symptom. The recognisable picture includes:
- Reduced sex drive and fewer spontaneous or morning erections.
- Erectile difficulty, often alongside the drop in desire rather than on its own.
- Persistent fatigue that does not lift with rest, and a general drop in drive and motivation.
- Loss of muscle and strength, and finding it harder to build or hold muscle despite training.
- Increased body fat, particularly around the middle.
- Low mood, irritability, or a flat, “blunted” feeling, and sometimes poorer concentration.
- Disrupted sleep, which then feeds back into the fatigue.
Less commonly, men notice reduced body or facial hair, breast tenderness or enlargement (gynaecomastia), or, when levels are very low, hot flushes. You do not need every symptom on this list. A consistent cluster, especially reduced libido plus fatigue plus loss of strength, is the pattern worth investigating. You can read more about the individual symptoms in our guides to low testosterone symptoms, low libido in men and erectile changes.
Why it happens
Testosterone naturally declines with age, gradually, at roughly one to two percent a year from around the age of 30 to 40. That slow drift is normal. What is not simply “age” is a level low enough to cause symptoms, and that often has a specific, treatable driver sitting on top of the age-related decline:
- Excess weight and metabolic syndrome. This is the single most common reversible contributor. Body fat converts testosterone to oestrogen and lowers the level, and the effect can be significant.
- Type 2 diabetes and insulin resistance, which are strongly linked to lower testosterone.
- Obstructive sleep apnoea, a frequently missed cause, particularly in men who snore heavily and wake unrefreshed.
- Certain medications, especially long-term opioids and anabolic or corticosteroid use.
- Problems in the testes themselves (primary), or in the pituitary and hypothalamus that signal them (secondary), including a raised prolactin from a pituitary cause.
- Chronic illness, high stress, and alcohol excess.
Sorting out which of these applies matters, because the fix is different each time, and some of the commonest causes respond well to lifestyle change alone.
Why the timing and detail of the test matter
A testosterone result is only meaningful if the sample is taken correctly, and if it is read alongside the right supporting markers. This is where a lot of testing falls down.
Testosterone follows a daily rhythm, peaking in the early morning and falling through the day, so a sample taken in the afternoon can read misleadingly low even in a perfectly healthy man. Food also transiently lowers it. For that reason, British Society for Sexual Medicine (BSSM) guidance is a fasting morning sample, drawn between 7 and 11 AM, with a low result confirmed on a second morning before a diagnosis is made, because a single low reading can be a blip caused by poor sleep, stress, or a recent illness.
Just as important is what else is measured. Total testosterone on its own can mislead, which is why a proper panel adds:
- Free testosterone, the small unbound fraction that is actually active, calculated from testosterone, SHBG and albumin.
- SHBG, the carrier protein that determines how much of your testosterone is available. Without it, a total-only reading can be wrong in both directions.
- LH and FSH, the pituitary signals that tell you why a level is low, distinguishing a testicular cause from a pituitary one.
What the numbers mean
BSSM regards a fasting morning total testosterone above 12 nmol/L as generally normal, and below 8 nmol/L as supporting a diagnosis of testosterone deficiency. Between 8 and 12 nmol/L is a grey zone, and this is exactly where the calculated free testosterone and your symptoms decide the picture.
The critical point is that a number in isolation does not make a diagnosis. A total testosterone of 10 nmol/L is “in range” on many lab reports, but in a man with clear symptoms and a low free testosterone it can be very relevant. This is why every testosterone blood test at WMG Health is interpreted by a GMC-registered doctor against your symptoms, not just ticked off against a reference range. For the full clinical detail, our clinical team has also published a clinical framework for managing low testosterone and hypogonadism.
What a complete testosterone workup looks like
| Marker | Why it is measured |
|---|---|
| Total testosterone | The first-line reading, drawn fasting in the morning |
| Free testosterone (calculated) | The active fraction; decisive in the 8–12 nmol/L grey zone |
| SHBG | Determines how much testosterone is bioavailable |
| LH and FSH | Classify the cause as testicular or pituitary |
| Prolactin, oestradiol (where indicated) | Investigate a secondary cause; relevant on treatment |
Our focused Testosterone Panel (£199) covers total testosterone, free testosterone and DHT, with LH, FSH, SHBG and prolactin added where a low result needs its cause explained. If your symptoms are broader than testosterone alone, the Hormone Specialist panel takes a wider view.
Where to get tested, and what happens next
You do not need a GP referral. Direct-access private testing means you can book a fasting morning appointment, have the right markers drawn in one visit, and get a clinician’s interpretation rather than a page of numbers.
If the workup confirms genuinely low testosterone with matching symptoms, the path forward depends on the cause:
- Address the reversible drivers first. Weight loss, better sleep (including treating sleep apnoea), resistance training, cutting excess alcohol, and reviewing any contributing medication can meaningfully raise testosterone on their own.
- Confirm before treating. A diagnosis needs two low morning samples, not one, which protects you from being started on treatment off the back of a rogue reading.
- Testosterone replacement therapy (TRT), where it is appropriate, is a specialist decision and requires ongoing monitoring (including testosterone, haematocrit and, where relevant, PSA), not a one-off prescription.
The reason to test rather than guess is simple: several of the commonest causes of low testosterone are treatable, and some are early signals of conditions like type 2 diabetes or sleep apnoea that are worth catching in their own right.
Getting tested at WMG Health
If the symptoms above sound familiar, particularly reduced libido, persistent fatigue, and loss of strength together, a properly timed blood test is the sensible first step. You can book a same-day, fasting morning appointment for a testosterone blood test at our Harley Street clinic. Results reviewed by a GMC-registered doctor, with a written explanation of what your numbers mean and no GP referral required.
Sources
- British Society for Sexual Medicine: Guidelines on Adult Testosterone Deficiency, with Statements for Practice. bssm.org.uk
- NICE Clinical Knowledge Summary: Erectile dysfunction. cks.nice.org.uk
- Society for Endocrinology: patient guidance on testosterone and hypogonadism. endocrinology.org
- NHS: Male menopause overview. nhs.uk
This article is for general information only and does not constitute clinical advice. If you have concerns about your symptoms, book an appointment or speak to your GP.