What Your Testosterone Blood Test Results Actually Mean

Most men who get a testosterone blood test receive a single number - total testosterone - and are told they're "normal" or "low". But that number tells you less than half the story.

Understanding your full hormone panel means understanding the entire system: what produces testosterone, what binds it and renders it inactive, what converts it into oestrogen, and what signals the brain is sending to regulate all of it.

Here's a complete breakdown of every marker on a comprehensive testosterone panel and what each one means.

Total Testosterone

This measures the total amount of testosterone circulating in your blood - including both the testosterone that's biologically active and the portion that's bound to proteins and unavailable to your cells.

Reference range: 8.0–29.0 nmol/L (UK) / 300–1,000 ng/dL (US)

What's optimal: Most men feel and function best with total testosterone in the range of 18–25 nmol/L. The lower end of the reference range (8–12 nmol/L) is technically "normal" but associated with symptoms of low testosterone in the majority of men.

What it doesn't tell you: Two men can have identical total testosterone levels but wildly different bioavailable testosterone. This is where SHBG matters enormously.

SHBG - Sex Hormone Binding Globulin

SHBG is a protein produced by the liver that binds testosterone (and other hormones) and renders them biologically inactive. Testosterone bound to SHBG cannot attach to androgen receptors in your cells - it's essentially locked up and unavailable.

Reference range: 18–54 nmol/L

The problem with high SHBG: High SHBG can make a man with "normal" total testosterone functionally testosterone deficient. The higher your SHBG, the more of your testosterone is bound and inactive.

High SHBG is associated with: ageing (SHBG increases by approximately 1–2% per year after 40), excess alcohol consumption, liver dysfunction, thyroid issues (both hyper- and hypothyroidism raise SHBG), low calorie intake, and very low body fat.

The problem with low SHBG: Below 18 nmol/L, SHBG may be too low, which is associated with insulin resistance, obesity, type 2 diabetes risk, and elevated cardiovascular markers. Low SHBG with normal total testosterone is a flag for metabolic dysfunction.

Free Testosterone

This is the fraction of testosterone that's not bound to any protein - roughly 1–4% of total testosterone. Free testosterone is what your cells can actually access and use.

Reference range: 0.17–0.60 nmol/L (varies by method used)

Why this matters: Free testosterone is the most clinically meaningful measure of androgenic activity. A man with total testosterone of 18 nmol/L and high SHBG might have lower free testosterone than a man with total testosterone of 14 nmol/L and low SHBG.

How to calculate it: Many labs now calculate free testosterone from total testosterone and SHBG using the Vermeulen equation rather than directly measuring it (direct measurement is less accurate). Either method provides a useful guide.

LH - Luteinising Hormone

LH is produced by the pituitary gland and signals the testes to produce testosterone. Understanding LH is critical for diagnosing why testosterone is low.

Reference range: 1.7–8.6 IU/L

High testosterone + high LH: Normal feedback loop, or possibly anabolic steroid use (where exogenous testosterone suppresses LH to near zero - if you see very low LH alongside very high testosterone, it's a flag)

Low testosterone + high LH: The testes are not responding to the signal. This is called primary hypogonadism - the problem is in the testes themselves, not the brain. Possible causes include varicocele, previous infection, or genetic conditions.

Low testosterone + low LH: The brain isn't sending the signal. This is secondary hypogonadism - the problem is in the hypothalamic-pituitary axis. Causes include: chronic stress (elevated cortisol suppresses GnRH, which drives LH), obesity, sleep deprivation, anabolic steroid history, or pituitary dysfunction.

This distinction matters because the treatment approaches differ completely.

FSH - Follicle Stimulating Hormone

FSH is produced alongside LH and primarily controls sperm production rather than testosterone synthesis. It's worth including if fertility is a concern or if there's a question about testicular function.

Reference range: 1.5–12.4 IU/L

Elevated FSH with low testosterone: Often indicates testicular failure (primary hypogonadism). The pituitary is pushing hard but the testes aren't producing.

Low FSH alongside low testosterone: Points to secondary hypogonadism - the pituitary itself is under-signalling.

Oestradiol (E2)

Men produce oestradiol (a form of oestrogen) through the aromatisation of testosterone - an enzyme called aromatase converts testosterone into oestradiol. This process is essential. Some oestradiol is necessary for bone density, cardiovascular health, and libido in men. But elevated oestradiol causes problems.

Reference range: 40–161 pmol/L in men (some labs use pg/mL: approximately 11–44 pg/mL)

High oestradiol symptoms: Reduced libido, emotional sensitivity, water retention, breast tissue development (gynaecomastia), fatigue.

What drives high oestradiol: Aromatase is most active in adipose (fat) tissue. Higher body fat percentage = more aromatase activity = more testosterone converting to oestradiol. This is why weight loss often raises effective testosterone even before any supplementation.

What to do about high oestradiol: Address body composition first. Zinc supplementation has mild aromatase-inhibiting properties. Avoid phytoestrogens (excess soy) and xenoestrogens (plastics, certain personal care products). Aggressive pharmaceutical aromatase inhibitors (anastrozole, etc.) should only be used under medical supervision.

Prolactin

Prolactin is a hormone primarily associated with lactation, but men produce it too. Elevated prolactin suppresses LH and FSH production, reducing testosterone.

Reference range: 86–324 mIU/L in men

Why it matters: Chronically elevated prolactin (hyperprolactinaemia) is an underdiagnosed cause of secondary hypogonadism in men. Causes include: pituitary adenoma (prolactinoma - a benign tumour, common), certain medications (antipsychotics, some antidepressants), chronic stress, hypothyroidism, and excessive alcohol.

If you have low LH, low testosterone, and unexplained symptoms, prolactin should be on your panel.

DHEA-S

DHEA-S (dehydroepiandrosterone sulphate) is a precursor hormone produced by the adrenal glands. It's converted into testosterone and oestrogen in peripheral tissues. DHEA-S declines sharply with age - peak levels occur around age 25 and fall by roughly 80% by age 70.

Reference range: 2.16–15.2 µmol/L (men, 40–49)

Low DHEA-S: Associated with accelerated ageing, fatigue, reduced anabolic capacity, and potentially lower testosterone production. Some research supports DHEA supplementation for men over 40 with documented deficiency, though evidence is mixed.

Cortisol

Cortisol (the stress hormone) directly antagonises testosterone production. Elevated cortisol suppresses the hypothalamic release of GnRH, which in turn reduces LH, which reduces testosterone synthesis. This is the biological mechanism behind the well-documented relationship between chronic stress and low testosterone.

Reference range: 140–700 nmol/L (morning, fasted)

Cortisol follows a diurnal rhythm - highest in the early morning, lowest at night. For accurate interpretation, blood draws should always be done fasted in the morning (before 10am).

Elevated morning cortisol: Chronic stress, poor sleep, high-intensity training without adequate recovery, caffeine excess, or adrenal dysfunction.

Getting a Full Panel Done

A comprehensive hormone panel including all of the above typically isn't available through a standard GP appointment. The NHS testosterone test (when you can get one) usually measures total testosterone only, missing SHBG, free testosterone, oestradiol, prolactin, and DHEA-S.

Private at-home testing services like Lola Health cover all of this with a single finger-prick blood collection and results within 48 hours. The Lola Health male health panel measures 40+ biomarkers including the full hormone profile above, plus thyroid, metabolic markers, vitamins, and a full blood count.

Testing twice a year - once in winter (when vitamin D is typically lowest and testosterone often follows) and once in summer - gives you a meaningful trend line rather than a single data point.

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Results should always be interpreted in context. This article is for educational purposes. If your results show significant abnormalities, speak with a GP or a men's health specialist.