Every men's health brand will sell you a testosterone number. None of them tell you what is making it that number. Total testosterone without SHBG, LH, FSH, cortisol, and thyroid context is a fact without a story. Here is how to test it properly.
Testing total testosterone alone is like checking your gross salary without knowing your tax rate. The number looks fine. The amount you take home might not be.
| Marker | What It Reveals | Why It Matters |
|---|---|---|
| Total testosterone | Total amount of testosterone in your blood | The starting point, but misleading alone. Does not tell you how much is actually available to your body. |
| SHBG | Sex hormone-binding globulin. The protein that binds testosterone and makes it unavailable. | High SHBG = less free testosterone. Elevated by the contraceptive pill, ageing, hyperthyroidism, liver disease. Low SHBG = more free testosterone but may indicate insulin resistance or hypothyroidism. |
| Free androgen index | Calculated ratio of total testosterone to SHBG | The best proxy for bioavailable testosterone. Two people with the same total can have vastly different FAI depending on their SHBG. This is the number that correlates with symptoms. |
| LH | Luteinising hormone from the pituitary gland | High LH + low testosterone = the testes are failing to respond (primary hypogonadism). Low LH + low testosterone = the brain is not sending the signal (secondary hypogonadism). This distinction completely changes the treatment approach. |
| FSH | Follicle-stimulating hormone from the pituitary | Works alongside LH to assess the HPG axis. In men, elevated FSH indicates testicular dysfunction. In women, rising FSH is the earliest sign of declining ovarian reserve. |
| Cortisol | Primary stress hormone from the adrenal glands | Chronic cortisol elevation directly suppresses testosterone production via the HPA axis. The most common reversible cause of low testosterone in young men. Without testing cortisol, you treat the symptom and miss the driver. |
| DHEA-S | Adrenal precursor hormone | Declines with age. Low DHEA-S with high cortisol indicates chronic adrenal stress. Provides context for both cortisol and testosterone interpretation. The stress axis marker nobody checks. |
TrueVitals Advanced (£269) includes total testosterone, SHBG, FAI, cortisol, and DHEA-S. The Ultimate panel (£349) adds LH, FSH, oestradiol, progesterone, and prolactin for the complete endocrine picture.
Low testosterone is a symptom with many possible drivers. A number on its own does not tell you which one. The markers around testosterone do.
Elevated cortisol directly suppresses gonadotropin-releasing hormone (GnRH) from the hypothalamus, which reduces LH output, which reduces testosterone production. This is the HPA axis overriding the HPG axis. It is your body prioritising survival over reproduction. The fix is not TRT. It is sleep, stress management, workload reduction, and training periodisation. Cortisol and DHEA-S reveal this pattern clearly.
Testosterone is produced primarily during deep sleep. One week of restricted sleep (5 hours per night) can reduce testosterone by 10 to 15%. This is independent of stress, diet, and exercise. If your cortisol is elevated and your testosterone is low, poor sleep quality may be the common driver. Your lifestyle quiz captures sleep data so your report can assess this.
Visceral fat converts testosterone to oestradiol via the aromatase enzyme. Insulin resistance reduces SHBG, which paradoxically increases free testosterone short-term but accelerates conversion to oestrogen and disrupts the HPG feedback loop. Testing insulin, HOMA-IR, and oestradiol alongside testosterone reveals this metabolic driver. Metabolic testing guide →
Hypothyroidism increases SHBG, reducing bioavailable testosterone. It also directly suppresses gonadal function. A man with a "normal" total testosterone of 16 nmol/L but subclinical hypothyroidism (low Free T3) may have low FAI and all the symptoms of low T, which resolve when the thyroid is treated. Without testing Free T3, the thyroid connection is invisible. Thyroid testing guide →
If LH and FSH are elevated but testosterone is still low, the pituitary is sending the signal but the testes are not responding. This is primary hypogonadism and may indicate testicular damage, genetic conditions (Klinefelter syndrome), or age-related Leydig cell decline. TRT may be appropriate here. Without LH and FSH, you cannot make this distinction.
If LH and FSH are both low alongside low testosterone, the brain is not sending the signal. Causes include chronic opioid use, pituitary tumours (prolactin check is essential here), head injury, severe caloric restriction, or extreme overtraining. This pathway requires different investigation and treatment than primary hypogonadism.
Testosterone is not just a male hormone. Women produce it in smaller quantities, and it plays an essential role in energy, libido, muscle maintenance, bone density, and mood.
Low testosterone in women causes fatigue, low libido, poor muscle tone, and flat mood. It is common post-menopause and increasingly recognised as a treatable condition. Some menopause specialists now prescribe testosterone alongside HRT.
High testosterone in women is associated with PCOS, causing acne, excess hair growth, irregular periods, and insulin resistance. Testing testosterone alongside insulin, HOMA-IR, LH, and FSH helps distinguish PCOS from other causes of high testosterone.
SHBG is critical for women. The oral contraceptive pill significantly raises SHBG, which binds testosterone and reduces the amount available. A woman on the pill with "normal" total testosterone may have a critically low free androgen index, explaining fatigue and low libido that started after beginning contraception. Without SHBG and FAI, this pattern is invisible.
Total testosterone. Maybe SHBG. No LH. No FSH. No cortisol. No DHEA-S. No thyroid. No oestradiol. Dashboard result. You get a number. You do not get an explanation. If it is low, you are told to see your GP. No analysis of what is causing it or what to do about it.
Total testosterone, SHBG, FAI, LH, FSH, oestradiol, cortisol, DHEA-S, prolactin, plus full thyroid, insulin, iron studies, and 100+ other markers. 30+ page AI-powered report explaining what is driving your levels, whether the cause is stress, metabolic, thyroid, or gonadal, and what to do about it. Medical professional review.
The price difference is approximately £250. The insight difference is the gap between a number and an explanation. For something as consequential as your hormonal health, the explanation is what matters. Full TrueVitals vs Numan comparison.
Testosterone peaks in the early morning and can drop 20-30% by the afternoon. Always test before 10am for a comparable result.
Fasting ensures insulin and glucose are accurate (both affect SHBG interpretation). Water is fine.
Alcohol acutely suppresses testosterone and elevates oestradiol. Even moderate drinking the night before distorts results.
Intense training temporarily suppresses testosterone and elevates cortisol. Test after a rest day for your baseline, not your training response.
Poor sleep directly reduces testosterone. An unusually bad night will produce a falsely low reading.
Testosterone fluctuates across the menstrual cycle. Day 2-5 gives the most consistent baseline. Report your cycle day so interpretation adjusts.
For men, the reference range is typically 8.6 to 29 nmol/L with optimal around 15 to 25. For women, 0.5 to 2.4 nmol/L with optimal varying by age and menstrual status. But total testosterone without SHBG and FAI context is unreliable. Your TrueVitals report shows both reference and optimal ranges with personalised interpretation.
The most common causes in men under 40 are chronic stress (elevated cortisol), poor sleep, excess body fat, insulin resistance, and overtraining. These are all reversible through lifestyle changes. LH, FSH, cortisol, DHEA-S, insulin, and thyroid testing identifies which driver is responsible. TRT should be a last resort, not a first response.
The NHS will test total testosterone if clinically indicated. They rarely test SHBG, FAI, or the supporting markers (LH, FSH, cortisol, DHEA-S) that explain why testosterone is what it is. A "normal" NHS testosterone result does not rule out a genuine hormonal problem if SHBG context is missing.
Testosterone replacement therapy (TRT) is a medical intervention that should only be considered after comprehensive testing confirms genuine hypogonadism and reversible causes (stress, sleep, body composition, thyroid) have been addressed. TRT suppresses natural production and is typically a lifelong commitment. Your TrueVitals report identifies the cause before jumping to treatment.
Morning before 10am, fasted, after a normal night's sleep, with 48 hours rest from intense exercise and alcohol. For women, day 2-5 of the menstrual cycle. Men can test any day provided the morning conditions are met.
Total testosterone, SHBG, FAI, LH, FSH, cortisol, DHEA-S, and 107 other markers. AI-powered analysis that tells you why, not just what. £349.
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