Why total testosterone alone is not enough, which markers men need for a complete picture, and how a comprehensive blood test identifies the real cause of symptoms like fatigue, low libido, and muscle loss.
If you suspect low testosterone, you need total testosterone, free androgen index, SHBG, LH, FSH, oestradiol, prolactin, cortisol, DHEA-S, thyroid function, and fasting insulin tested together — not just total testosterone in isolation. A GP will typically test total testosterone only, and if it falls within the broad reference range of 8-29 nmol/L, you will be told you are normal. The TrueVitals Ultimate panel tests all of these as part of a 110-biomarker panel with a 60-page personalised report for £349.
Low testosterone affects an estimated 1 in 5 men over 30, but the way it is investigated in the UK means most cases are either missed entirely or misattributed to "stress" or "ageing." The reason is simple: the standard approach of testing total testosterone alone misses the majority of the picture.
Why total testosterone alone is misleading:
Total testosterone measures all testosterone in your blood, but approximately 98% of it is bound to proteins and unavailable to your tissues. Only the free fraction — roughly 2% — is biologically active. Two men can have identical total testosterone of 18 nmol/L, but if one has an SHBG of 25 and the other has an SHBG of 60, their free testosterone levels are dramatically different. The first man has adequate free testosterone. The second is functionally deficient despite a "normal" total. Free androgen index, calculated from total testosterone and SHBG, reveals this difference. Most GPs do not test SHBG or calculate free androgen index.
The markers that actually matter:
SHBG (sex hormone binding globulin) binds testosterone and reduces its bioavailability. High SHBG is common in men who are lean, stressed, hyperthyroid, or taking certain medications. Low SHBG is common in insulin resistance, obesity, and type 2 diabetes. Without knowing SHBG, total testosterone is an incomplete measurement.
LH and FSH from the pituitary gland tell the testes to produce testosterone. If total testosterone is low and LH/FSH are high, the problem is in the testes (primary hypogonadism). If total testosterone is low and LH/FSH are also low, the problem is in the brain not sending the signal (secondary hypogonadism). This distinction is critical because the causes and treatments are entirely different. Secondary hypogonadism is often caused by stress, poor sleep, obesity, or medication — all potentially reversible without testosterone replacement therapy. Your GP almost never tests LH and FSH when investigating testosterone complaints.
Oestradiol in men is produced by converting testosterone via the aromatase enzyme. Elevated oestradiol in men causes breast tissue growth, water retention, emotional sensitivity, and can paradoxically worsen symptoms of low testosterone. Aromatase activity increases with body fat, which is why overweight men often have both low testosterone and high oestradiol. This is a treatable pattern but invisible without testing.
Prolactin is a pituitary hormone that suppresses testosterone when elevated. High prolactin in men can cause low libido, erectile dysfunction, fatigue, and rarely visual disturbances if caused by a pituitary adenoma. It is frequently elevated by stress, sleep deprivation, and certain medications including antidepressants.
Cortisol directly suppresses testosterone production. A man with chronically elevated cortisol from work stress, poor sleep, or overtraining will often present with low testosterone as a secondary effect. Treating the cortisol issue — through stress management, sleep improvement, or training modification — can restore testosterone without any medical intervention. But if cortisol is never tested, this connection is never made.
DHEA-S is an adrenal precursor hormone that declines with age and chronic stress. Low DHEA-S alongside low testosterone and elevated cortisol suggests adrenal depletion rather than testicular failure — again, a fundamentally different problem requiring a different approach.
Thyroid function affects testosterone through multiple pathways. Hyperthyroidism raises SHBG, reducing free testosterone. Hypothyroidism reduces metabolic rate and can directly impair testicular function. A complete thyroid panel including Free T3 and antibodies is essential context for interpreting testosterone results.
Fasting insulin matters because insulin resistance drives down SHBG, increases aromatase activity (converting more testosterone to oestradiol), and promotes abdominal fat gain which further worsens the hormonal picture. Many men with "low testosterone" actually have insulin resistance as the root cause.
What happens when you only test total testosterone:
Your GP tests total testosterone. It comes back at 14 nmol/L. The reference range starts at 8. You are told you are normal. But your SHBG is 55 (high, binding most of your testosterone), your cortisol is elevated (suppressing production), your insulin is 22 (insulin resistant, driving down SHBG paradoxically while increasing aromatisation), and your DHEA-S is low (adrenal depletion). The actual picture is a man with functionally low testosterone driven by stress and metabolic dysfunction — entirely treatable through lifestyle intervention. But none of this is visible from total testosterone alone.
The TrueVitals Ultimate panel tests every marker discussed above plus a complete metabolic profile, liver function, kidney function, inflammation markers, vitamins, iron studies, and more — 110 biomarkers in total. The 60-page personalised report explains how your testosterone results connect to your cortisol, SHBG, insulin, thyroid, and lifestyle data, with targeted recommendations for what to do about it.