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Your testosterone result came back. You have a number. The problem is you do not know what it means, because the reference range your lab printed next to it covers 21 nmol/L of variation and calls all of it normal.
This is how to actually read the panel.
Why the NHS reference range is nearly useless
The NHS normal range for total testosterone is 8 to 29 nmol/L. A 21 nmol/L spread that classifies both a man who feels terrible and a man who feels excellent as "normal."
A man at 9 nmol/L and a man at 26 nmol/L will have completely different energy levels, libido, body composition, and mood, and both will receive the same letter saying their results are normal.
The reference range exists to identify the bottom 2.5% and top 2.5% of the population, not to tell you whether your hormonal environment is optimal for you specifically.
The markers that actually matter
Total testosterone
The starting number. Measured in nmol/L in the UK (some US labs use ng/dL, multiply by 28.8 to convert). Tested in the morning (fasted, ideally before 10am) because testosterone follows a diurnal rhythm and is highest in the early morning.
Broad benchmarks for total testosterone in adult men:
Do not read these ranges as definitive. They are context, not verdict.
SHBG (sex hormone-binding globulin)
This is the marker most GPs do not check, and the one that changes the interpretation of total testosterone most dramatically.
SHBG is a protein produced in the liver that binds testosterone (and oestradiol) and renders it biologically inactive. Only unbound (free) testosterone can enter cells and produce effects.
High SHBG: your total testosterone looks acceptable but most of it is locked up. Free testosterone is low. You feel the effects of low testosterone despite a normal total reading. This is common in men with elevated thyroid hormone, liver issues, or who are on certain medications.
Low SHBG: your total testosterone looks borderline but more of it is free and active. You may feel better than your total testosterone suggests. Associated with obesity, insulin resistance, and metabolic syndrome.
Normal SHBG for adult men: approximately 18 to 54 nmol/L.
My first test came back 8.4 nmol/L total testosterone. My GP said normal (just above the 8 nmol/L floor). But my SHBG was 67 nmol/L, well above range, which meant my free testosterone was genuinely suppressed. Without that SHBG number, I would have accepted a result that was actually the beginning of a diagnostic picture. That result changed everything that came next.
Free testosterone
Free testosterone is not usually measured directly, it is calculated from total testosterone and SHBG using a validated formula. This calculated free testosterone is what most labs report.
Normal free testosterone: approximately 0.2 to 0.6 nmol/L (varies by lab and method).
If your total testosterone is in the mid-normal range but your SHBG is elevated, your free testosterone may be genuinely low, and this is the number that explains your symptoms. If your GP only tested total testosterone, they may have missed this entirely.
LH and FSH
LH (luteinising hormone) and FSH (follicle-stimulating hormone) are pituitary hormones that signal the testes to produce testosterone. Testing these tells you whether a testosterone problem is testicular (primary hypogonadism) or pituitary (secondary hypogonadism).
High LH + low testosterone: primary hypogonadism. The pituitary is shouting at the testes, but the testes are not responding. The problem is at the testicular level.
Low LH + low testosterone: secondary hypogonadism. The pituitary is not sending the signal. The problem is upstream, at the hypothalamic or pituitary level. This pattern requires different investigation and may affect treatment options (HCG may be used instead of or alongside testosterone).
Normal LH + low-normal testosterone: functional suppression, often stress, sleep deprivation, overtraining, or elevated cortisol. Address the underlying cause first before considering hormonal intervention.
Oestradiol
Men produce oestradiol (a form of oestrogen) through aromatisation of testosterone, primarily in fat tissue. Some oestradiol is essential for libido, bone density, cognitive function, and cardiovascular health. Too much causes problems: water retention, gynecomastia (breast tissue development), and low libido, counterintuitively similar to the symptoms of low testosterone.
Checking oestradiol in context with total testosterone gives you your testosterone-to-oestradiol ratio. A rising ratio as testosterone declines is a common pattern in men with increasing body fat.
Normal oestradiol for adult men: approximately 40 to 160 pmol/L.
If you are on TRT, oestradiol monitoring is essential. Exogenous testosterone aromatises to oestradiol and without monitoring, oestradiol can rise significantly.
Prolactin
Elevated prolactin (hyperprolactinaemia) suppresses LH and FSH, which reduces testosterone. The most common cause is a pituitary microadenoma (benign tumour). If your LH and FSH are both low and testosterone is suppressed, prolactin should be checked.
Mildly elevated prolactin can also be caused by stress, exercise, sexual activity, or certain medications, so interpretation requires context.
How to read your results together
A worked example:
- Total testosterone: 10.3 nmol/L
- SHBG: 62 nmol/L (elevated)
- Free testosterone: 0.19 nmol/L (low)
- LH: 4.2 IU/L (normal)
- FSH: 3.8 IU/L (normal)
- Oestradiol: 68 pmol/L (normal)
Interpretation: secondary pattern with possible hypothalamic suppression or elevated SHBG driving the picture. LH is not elevated (ruling out primary hypogonadism), and the very high SHBG is pulling free testosterone below range despite total testosterone being technically within the NHS range. This person will feel symptomatic and their total testosterone reading alone would not have flagged a problem.
Total testosterone without SHBG and LH is a starting point, not an answer. If you have been told your results are normal but you feel symptomatic, request the full panel, specifically SHBG, LH, FSH, and free testosterone. The numbers that explain symptoms are often the ones that were not tested.
When and how to test
Test in the morning, ideally between 8am and 10am. Testosterone peaks in the early morning and drops through the day, afternoon tests can read 20 to 30% lower than morning results on the same person.
Test fasted or after a light breakfast only. Significant food intake can temporarily suppress testosterone.
Do not test immediately after intense exercise or illness, both suppress testosterone acutely.
If your first result is low or borderline, repeat it. One low reading is not a diagnosis. Two low readings, both in the morning, both fasted, taken a few weeks apart, with matching symptoms, that is a clinical picture.
For a full comparison of home blood testing services, the home blood test comparison for UK men covers Medichecks, Forth, Lola Health, and Thriva in detail.
Further reading
- Best home blood tests for men UK 2026, all services compared
- Medichecks review, which panel to order
- Best TRT clinics UK, if your results show low testosterone
- Best testosterone support supplements UK
Affiliate disclosure: This article contains affiliate links to Medichecks via Awin. If you purchase through these links, Male Optimal earns a small commission at no extra cost to you. This does not affect recommendations.
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