Optimal testosterone ranges for men — beyond the reference range

The reference range problem

The 300–1000 ng/dL total testosterone range you see on virtually every lab report is a statistical artefact, not a clinical target. It was constructed from cohorts that included men in their seventies, men with untreated metabolic syndrome, men with subclinical hypogonadism, and men whose chronic illness had already collapsed their endocrine output. The lower bound of 300 ng/dL marks the 2.5th percentile of that mixed population — it does not mark the threshold below which physiology begins to fail. By the time you cross it, you have crossed it by a long way.

Studies that stratify by symptom burden rather than statistical distribution find that libido, erectile function, and morning erections begin to deteriorate below roughly 400–450 ng/dL, depressive symptoms and loss of vigour cluster below 350–400 ng/dL, and metabolic markers (visceral fat, insulin sensitivity, lipid profile) deteriorate progressively as totals fall below 500 ng/dL. The 300 ng/dL line is not a cliff. It is a marker of severe deficit in a population that already accepts moderate deficit as normal.

SHBG: the binding protein that determines what testosterone actually does

Sex hormone binding globulin is the variable most panels under-weight and most clinicians under-explain. Roughly 98% of circulating testosterone is bound — about 44–65% to SHBG with high affinity, and most of the rest to albumin with low affinity. Only the unbound fraction (typically 1–2%) is freely bioavailable to tissues. SHBG therefore sets the gain on whatever total testosterone you produce.

What drives SHBG up: elevated thyroid hormone (hyperthyroid states, over-replacement on T4), low insulin states (caloric restriction, very-low-carbohydrate diets, type 1 diabetes), liver disease and cholestasis, oestrogen excess, advancing age, and certain anticonvulsants. High SHBG sequesters testosterone — your total may read 700 ng/dL while your free fraction sits at the floor of the reference range. You will be symptomatic at a "normal" total.

What drives SHBG down: insulin resistance and hyperinsulinaemia, central adiposity, hypothyroidism, exogenous androgens (especially oral 17α-alkylated compounds), elevated prolactin, growth hormone excess, and nephrotic syndrome. Low SHBG is the more common finding in metabolically unwell men. It artificially inflates the free fraction in the short term and is itself a predictive biomarker for incident type 2 diabetes and cardiovascular events.

Because SHBG is exquisitely sensitive to thyroid status, a low or borderline reading should prompt a thyroid panel review — TSH, free T4, free T3, and reverse T3. Subclinical hypothyroidism with normal TSH but suppressed free T3 will pull SHBG down and distort every downstream interpretation.

Free testosterone: the bioavailable fraction

Free testosterone is what reaches the androgen receptor. Two methods dominate: direct immunoassay and calculated free testosterone derived from total T, SHBG, and albumin via the Vermeulen equation. The direct immunoassay is widely available, cheap, and unreliable — analogue methods systematically misreport at the low end and correlate poorly with equilibrium dialysis (the reference standard).

Calculated free testosterone, despite being a model rather than a measurement, tracks equilibrium dialysis far more faithfully across the physiological range. If you are interpreting a panel and you see a direct free T result that contradicts your calculated value, trust the calculation. The inputs (total T by LC-MS/MS, SHBG, albumin) are individually robust; the equation that combines them is well-validated.

For optimisation purposes, free testosterone in the upper quartile of the reference range — roughly 20–30 pg/mL when calculated — corresponds to the symptom-free zone in most men. Below 12 pg/mL the symptom prevalence rises sharply regardless of where the total sits.

The LH/FSH ratio as an HPG axis health indicator

LH and FSH are upstream signals from the pituitary. They tell you whether the gonads are being asked to work harder, less hard, or normally. Reading them in isolation is meaningless; reading them against total testosterone reveals the lesion.

• Primary hypogonadism (testicular failure): low total T, elevated LH (often >9 IU/L) and FSH. The pituitary is screaming and the testes are not responding. Causes include Klinefelter, prior orchitis, varicocele, chemotherapy exposure, ageing Leydig cell decline, and trauma.
• Secondary hypogonadism (central): low total T with low or inappropriately normal LH and FSH (typically both <4 IU/L). The signal is missing. Causes include hyperprolactinaemia, opioid use, chronic stress and HPA-axis dominance, sleep apnoea, severe caloric deficit, and pituitary lesions.
• Compensated state: normal total T with elevated LH. The testes are working hard to maintain output. This is an early warning of declining testicular reserve.
• Suppressed state: low or normal total T with LH and FSH near zero (<1 IU/L). Almost always exogenous androgen exposure, including transdermal contamination, prohormones, or undisclosed TRT.

The LH:FSH ratio itself is more diagnostic in women, but in men a markedly elevated FSH with normal LH suggests selective seminiferous tubule damage (often relevant for fertility) while preserved Leydig cell function. Cortisol-driven HPG suppression is a common and under-recognised cause of low-normal LH with low-normal T — see the cortisol and DHEA panel for the adrenal axis interaction.

Estradiol: the necessary balance

Estradiol in men is not a contaminant. It is required for bone mineral density, vascular endothelial function, libido, lipid handling, joint integrity, and central nervous system function. Men aromatase a small fraction of their testosterone to estradiol via adipose tissue, brain, bone, and gonads. The historical instinct to suppress E2 aggressively with aromatase inhibitors has produced a generation of men with brittle bones, joint pain, anhedonia, and dyslipidaemia at "perfect" testosterone levels.

The optimal E2 range for most men sits at 20–30 pg/mL by LC-MS/MS (the sensitive assay; standard immunoassay over-reads in men and should be specifically requested as "estradiol, sensitive" or "ultra-sensitive"). Below 15 pg/mL libido collapses, joint symptoms emerge, and bone turnover markers rise. Above 40 pg/mL water retention, gynaecomastia risk, and mood changes become more probable.

The clinically useful number is the T:E2 ratio, not E2 alone. A man with total T of 800 ng/dL and E2 of 35 pg/mL has a healthier ratio than one with total T of 450 ng/dL and E2 of 30 pg/mL, despite the absolute E2 being higher in the first case. Aromatase activity scales with adipose mass and inflammation; lowering body fat is a more durable E2 lever than pharmacological suppression.

Optimisation ranges versus reference ranges

The evidence on where total and free testosterone should sit for optimal function — as opposed to the absence of overt deficiency — is more consistent than is often acknowledged. Cognitive performance, mood stability, body composition, libido, erectile function, and recovery capacity all show dose-response relationships that flatten somewhere in the upper-normal range and do not improve further at supraphysiological levels.

For most men under 50, the functional sweet spot looks like:

• Total testosterone: 600–900 ng/dL
• Calculated free testosterone: 20–30 pg/mL
• SHBG: 20–35 nmol/L
• Estradiol (sensitive): 20–30 pg/mL
• LH: 3–6 IU/L (if endogenous)
• FSH: 2–7 IU/L

Pushing total T above 1000 ng/dL adds little to subjective wellbeing and adds polycythaemia risk, sleep disruption, acne, and accelerated androgenetic alopecia in genetically susceptible men. The diminishing returns curve is real.

Reading the full panel as a system

A single hormone reading is a snapshot. The diagnostic information lives in the relationships:

1. Total T ÷ SHBG gives you the free androgen ratio. If total is 600 ng/dL and SHBG is 70 nmol/L, your free fraction is going to disappoint regardless of the headline number.
2. Free T confirms what the ratio predicted. Calculated and direct should roughly agree; if they diverge, trust the calculation.
3. E2 ÷ T ratio flags aromatase pressure. A rising E2 with stable T points to adipose-driven conversion.
4. LH and FSH localise any deficit to gonads (high LH/FSH) or hypothalamus-pituitary (low LH/FSH).
5. Pattern recognition: Low T + high SHBG + normal LH = hypothyroid or under-eating picture. Low T + low SHBG + low LH = metabolic and cortisol-driven picture. Low T + high LH + normal SHBG = primary testicular failure. Normal T + low free T + high SHBG = pseudo-deficiency from binding excess.

For how the testosterone panel integrates with the rest of a comprehensive blood panel — including metabolic markers, liver function, and the CBC — see the complete guide to interpreting blood test results. Iron status is also worth monitoring alongside testosterone: iron deficiency suppresses haemoglobin and oxygen-carrying capacity, which compounds fatigue symptoms and can be misattributed to low T — see the ferritin and iron panel guide for interpretation.

Protocol monitoring: what changes after intervention

Once an exogenous androgen is introduced — whether testosterone esters, gels, or pellets — the interpretation framework changes. LH and FSH should drop to near-zero within weeks; persistent LH above 1 IU/L on therapy suggests under-dosing or absorption failure. SHBG typically falls by 20–40% on TRT, which means total T targets must rise to maintain the same free fraction. A total of 700 ng/dL with SHBG of 18 nmol/L on therapy delivers a higher free T than the same total at SHBG 40 off therapy.

E2 dynamics shift as well. Aromatisation rises with the dose and especially with the ester peak; trough-to-peak E2 swings of 20–40 pg/mL are common on weekly intramuscular protocols. More frequent, smaller injections flatten this curve and reduce the perceived need for aromatase inhibition.

For men running peptide protocols that elevate growth hormone or IGF-1, SHBG tends to fall further and free T rises proportionally; this is one mechanism by which GH secretagogues subjectively potentiate androgen effects. IGF-1 should be tracked alongside the gonadal panel — values pushed above the age-adjusted reference range warrant review.

Trough timing matters. For weekly esters, draw immediately before the next injection to capture the trough; for daily transdermal, draw 2–4 hours post-application; for endogenous monitoring, draw between 7am and 10am fasted, on two separate occasions, with no recent acute illness or sleep deprivation. Single readings are noise; serial readings are signal.

For Australians monitoring testosterone, SHBG, LH, FSH, and estradiol on a self-directed basis, our guide to private blood testing in Australia covers how to access a full male hormone panel without a GP referral — including which providers carry these markers, how morning draw timing works in a walk-in setting, and what a comprehensive panel typically costs out of pocket.