There is no single number that qualifies you for testosterone replacement therapy. UK guidance works with bands: a level below which deficiency is likely, a grey zone where free testosterone and symptoms decide, and a level above which something else is probably going on. This page sets out those bands, the free testosterone thresholds that matter inside the grey zone, and how the NHS and private clinics apply them differently.
It sits alongside our full guide to how to get TRT in the UK, which covers the whole pathway. Here we stay on the numbers.
The total testosterone thresholds UK doctors use
UK practice follows the British Society for Sexual Medicine guidelines, supported by the Endocrine Society's clinical practice guideline. Both ask for total testosterone to be measured on two separate mornings before anything is decided, and both read the result in bands rather than against a single cut-off.
Try your number
Slide to your total testosterone and read what that band usually means. Add SHBG for free testosterone.
≈ 288 ng/dL
The grey zone
Whether this is low for you depends on your SHBG, your calculated free testosterone and your symptoms. A calculated free testosterone below 0.225 nmol/L supports treatment in a man with symptoms. Two men with this total can be in very different positions.
- NHS, typically
- Often repeated and watched; treatment depends on the endocrinologist and local policy.
- Private clinic (Arc)
- Free testosterone and symptoms decide; a monitored trial is often appropriate.
Uses the Vermeulen equation, the same as our calculator.
This describes how UK guidance reads a confirmed result. It is not a diagnosis. A single sample, an afternoon sample or a result during illness needs repeating before any of this applies.
- Below 8
- Testosterone deficiency. Treatment is usually appropriate where symptoms are present.
- 8 to 12
- The grey zone. Free testosterone and symptom burden determine the decision. A trial of treatment may be appropriate.
- 12 to 15
- Treatment at the clinician's discretion where symptoms are significant and free testosterone supports it.
- Above 15
- Deficiency unlikely. Symptoms should be investigated for other causes.
Two points about that scale. First, the bands describe likelihood, not permission. A man at 7 nmol/L with no symptoms does not need treatment; a man at 13 nmol/L with a free testosterone in the deficient range and a clear symptom picture may. Second, the thresholds are for a properly timed, repeated sample. One afternoon result from a GP surgery is a reason to test again, not a diagnosis either way.
Free testosterone: the number that decides the grey zone
Most of the testosterone in your blood is bound to sex hormone binding globulin (SHBG) and is not available to your tissues. Two men with an identical total of 11 nmol/L can have very different free levels if one has an SHBG of 25 and the other an SHBG of 70. The second man is, in practical terms, deficient. If nobody measures SHBG, he is told he is normal.
For that reason the BSSM treats a calculated free testosterone below 0.225 nmol/L (225 pmol/L, roughly 65 pg/mL) as supporting treatment in a man with symptoms, whatever his total. The 2018 International Consultation for Sexual Medicine adds its own grey zone between about 0.225 and 0.347 nmol/L (65 to 100 pg/mL), where a symptomatic man can be offered a trial of treatment at the doctor's discretion.
Free testosterone is calculated from total testosterone, SHBG and albumin using the Vermeulen equation. Our free testosterone calculator does the arithmetic, and our SHBG guide explains what pushes SHBG up or down. If your results are in ng/dL or pg/mL, the testosterone unit converter translates them into the UK units above.
How the sample has to be taken
Testosterone follows a daily rhythm and peaks in the morning, so the guidelines ask for samples between 7am and 11am on two different days. The morning peak flattens with age, which is why we accept a test before midday if you are under 40 and before 2pm if you are 40 or over, and confirm any low result with a second sample. You do not need to fast.
A single low reading is never enough. Illness, a bad night's sleep, a heavy training session the day before or a recent large meal can all pull a result down temporarily. The repeat sample is what turns a number into a diagnosis.
What else has to be on the panel
A total testosterone on its own cannot tell you whether you qualify. The minimum a defensible assessment measures is:
- Total testosterone, repeated on a second morning.
- SHBG and albumin, so free testosterone can be calculated.
- LH and FSH, which separate a testicular problem (primary hypogonadism, high LH) from a signalling problem (secondary hypogonadism, low or normal LH). Secondary causes such as sleep apnoea, excess weight and some medications can be reversible.
- Prolactin, to exclude a pituitary cause when LH is low.
- Oestradiol, as a baseline for monitoring.
- Full blood count, particularly haematocrit, which rises on treatment.
- PSA in men over 40, before any testosterone is prescribed.
- Thyroid function, HbA1c, lipids, ferritin and vitamin D, because several of these mimic the symptoms of low testosterone.
Our guide to testosterone blood test results walks through how to read each of these, and normal testosterone levels by age puts your total in context.
NHS and private thresholds in practice
The guideline bands are the same whoever you see. What differs is how far into the grey zone a clinician is willing to go.
| Result | NHS (typical) | Private clinic (Arc) |
|---|---|---|
| Below 8 nmol/L with symptoms | Referral to endocrinology, treatment usually offered | Treatment offered after the repeat sample and full panel |
| 8 to 12 nmol/L with symptoms | Often repeated and watched; treatment depends on the endocrinologist and local policy | Free testosterone and symptoms decide; a monitored trial is often appropriate |
| 12 to 15 nmol/L with symptoms | Rarely treated | Possible at the doctor's discretion where free testosterone is low and symptoms significant |
| Above 15 nmol/L | Not treated; other causes investigated | Not treated; other causes investigated |
There is more on the NHS route, including what a GP needs to see before referring, in can you get TRT on the NHS?. The costs of going private are set out in how much TRT costs in the UK.
Numbers that can rule treatment out, for now
Qualifying is not only about testosterone being low. A responsible clinic will delay or decline treatment where:
- Haematocrit is already high (commonly above 0.50), because testosterone raises red cell count further.
- PSA is raised or a prostate examination is abnormal, until urology has looked.
- Sleep apnoea is untreated, since testosterone can worsen it and treating it can restore your own production.
- You want children in the near future, because testosterone suppresses sperm production. hCG or enclomiphene may be discussed instead; see TRT and fertility.
- A pituitary cause is suspected (low LH with high prolactin), which needs investigating first.
None of these are permanent bars. They are the reasons a good assessment takes longer than a single blood test and a prescription.
Not sure where your levels sit?
Our enhanced blood test covers everything on the panel above, with a doctor's written review.
Sources
British Society for Sexual Medicine, guidelines on the management of testosterone deficiency; Bhasin S et al., Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline, JCEM 2018; Hackett G et al., International Consultation for Sexual Medicine, 2018; Vermeulen A et al., A critical evaluation of simple methods for the estimation of free testosterone in serum, JCEM 1999.
