Low testosterone — male hypogonadism — is common, frequently under-recognised, and often confused with normal ageing. This article sets out what hypogonadism actually is, how it is diagnosed under current European Association of Urology (EAU) and Endocrine Society guidance, and how testosterone replacement therapy is used and monitored safely, including the specific products licensed for use in Ireland.
What Is Male Hypogonadism?
Male hypogonadism is a clinical syndrome in which the testes fail to produce adequate testosterone, adequate sperm, or both. A proper diagnosis requires two things together: persistent symptoms consistent with testosterone deficiency, and biochemical confirmation of low testosterone on repeat testing. Neither alone is sufficient — symptoms without a confirmed low level should not be treated as hypogonadism, and an isolated low reading without symptoms does not automatically require treatment.
Hypogonadism is classified by where the underlying problem lies:
- Primary (hypergonadotropic) hypogonadism — testicular failure. The testes do not respond normally to pituitary stimulation. Causes include Klinefelter syndrome, previous chemotherapy or radiotherapy, mumps orchitis, and undescended testes (cryptorchidism).
- Secondary (hypogonadotropic) hypogonadism — insufficient stimulation from the pituitary or hypothalamus. Causes include pituitary tumours, haemochromatosis, opioid use, and idiopathic hypogonadotropic hypogonadism.
- Functional hypogonadism — low testosterone in the absence of any structural abnormality of the reproductive axis, driven mainly by obesity, poorly controlled Type 2 diabetes, or other significant comorbidity. The 2026 EAU guidance is explicit that this group should have the underlying condition treated first, since testosterone often normalises with weight loss or improved metabolic control without needing testosterone therapy itself.
Where age-related testicular decline combines with specific symptoms in an older man, this is termed late-onset hypogonadism (LOH). It sits on a spectrum with functional hypogonadism and requires the same careful biochemical confirmation before treatment — testosterone decline with age is expected, but not every man with a lower level needs, or benefits from, testosterone therapy.
Recognising the Symptoms
Symptoms of testosterone deficiency are non-specific and overlap with many other conditions, which is exactly why biochemical confirmation is essential before treatment is considered:
- Sexual symptoms: reduced libido, erectile dysfunction, fewer spontaneous erections
- Energy and mood: persistent fatigue, low mood, reduced motivation, poor concentration
- Physical changes: reduced muscle mass and strength, increased abdominal fat, reduced body or facial hair
- Bone health: reduced bone density, osteopenia or osteoporosis
- Other: hot flushes or sweating, reduced testicular volume
Many men live with clinically significant testosterone deficiency for years without it being investigated, often because symptoms are attributed to stress, ageing or lifestyle alone.
Diagnosis: What the 2026 Guidelines Say
Confirming hypogonadism is a two-step process: establishing a genuinely low testosterone level on repeat testing, then working out why.
| Step | Current Guidance |
|---|---|
| Sample timing | Early morning (testosterone is highest on waking and falls through the day), fasting, on at least two separate occasions. |
| Total testosterone threshold | ≤12 nmol/L (≈346 ng/dL) supports a diagnosis of symptomatic hypogonadism per the EAU 2026 update. Greatest treatment benefit is seen below 8 nmol/L. |
| Free testosterone | Calculated using SHBG; a threshold of around 220 pmol/L (≈6.4 ng/dL) is used where binding proteins are altered — notably in obesity, where SHBG is often lower and total testosterone can underestimate true deficiency. |
| LH / FSH | Distinguishes primary (raised LH/FSH) from secondary (low or inappropriately normal LH/FSH) hypogonadism, and directs further pituitary assessment where needed. |
It is worth being transparent that diagnostic thresholds are not perfectly standardised worldwide. The Endocrine Society's guideline uses a lower total testosterone cut-off (264 ng/dL, ≈9.2 nmol/L) and the American Urological Association uses 300 ng/dL (≈10.4 nmol/L), compared with the EAU's 12 nmol/L. This is one reason a single number should never be read in isolation — it must be interpreted alongside symptoms, repeat testing, and the individual clinical picture, not treated as a rigid cut-off.
Testosterone Replacement Therapy
Where hypogonadism is genuinely confirmed, testosterone replacement therapy (TRT) can meaningfully improve energy, mood, libido, erectile function, muscle mass and bone density. Two testosterone products are HPRA-licensed for use in Ireland:
- Testogel — a daily transdermal gel, generally the preferred starting option under current European Academy of Andrology guidance, allowing dose titration and easy discontinuation if needed.
- Nebido — a long-acting intramuscular injection, typically given roughly every 10–14 weeks once levels are stabilised, suited to men who prefer infrequent dosing over daily application.
The choice between formulations depends on patient preference, lifestyle, and monitoring practicalities, and is discussed individually rather than defaulted to one option.
Who Should Not Start Testosterone Therapy
A number of situations mean testosterone therapy should not be started, or should only be considered after specialist assessment:
- Untreated or active prostate cancer, or breast cancer
- A palpable prostate abnormality, or an unexplained elevated PSA pending urological review
- A desire to father a child in the near term (testosterone suppresses natural sperm production)
- Untreated severe obstructive sleep apnoea
- Uncontrolled heart failure
- Myocardial infarction or stroke within the previous six months
- Thrombophilia (increased clotting tendency)
- Unexplained elevated haematocrit (raised red blood cell concentration)
Testosterone therapy in men with a prostate cancer history was long considered an absolute contraindication. Evidence in carefully selected men — for example those on active surveillance or with a sustained undetectable PSA after definitive treatment — has evolved in recent years, and testosterone therapy is now cautiously considered in some such cases. This remains a specialist, individualised decision made jointly with urology, not a routine approach, and should never be pursued outside proper multidisciplinary assessment.
Monitoring Once Treatment Starts
Safe prescribing depends on structured follow-up, not a one-off decision to start:
- PSA: baseline testing from age 40, repeated periodically. Findings prompting urological referral include a PSA velocity above 0.4 ng/mL per year, an absolute PSA above 4.0 ng/mL, or a rise of more than 1.4 ng/mL from baseline.
- Haematocrit: testosterone stimulates red blood cell production. A haematocrit above 54% requires stopping or reducing treatment, and investigating for contributing causes such as undiagnosed sleep apnoea.
- Lipids and general review: along with ongoing symptom and testosterone-level review to confirm the treatment is achieving its intended benefit.
Fertility Considerations
Because exogenous testosterone suppresses the pituitary signals (LH and FSH) that drive natural sperm production, standard TRT is not appropriate for men who are actively trying to conceive. Where fertility is a current priority, alternatives such as gonadotropin therapy, or referral to a reproductive specialist, are considered instead — this should always be raised and discussed before treatment begins, not after.
The Metabolic Connection
Hypogonadism has significant cardiometabolic associations. Low testosterone is more common in men with obesity and Type 2 diabetes, and the relationship runs in both directions — obesity lowers testosterone (partly through functional hypogonadism), and low testosterone can, in turn, worsen fat gain and insulin resistance. This is why assessment of testosterone deficiency at our clinic includes a wider metabolic review, and why weight and metabolic management is often part of treating functional hypogonadism, sometimes without testosterone therapy being needed at all.
Frequently Asked Questions
What is male hypogonadism?
Male hypogonadism is a clinical syndrome combining persistent symptoms (such as low libido, erectile dysfunction, fatigue or reduced muscle mass) with biochemically confirmed low testosterone. It is classified as primary (hypergonadotropic), where the testes themselves fail to produce enough testosterone, or secondary (hypogonadotropic), where the failure lies in the pituitary or hypothalamus. A third category, functional hypogonadism, is increasingly recognised — low testosterone driven mainly by obesity or other comorbidities rather than a structural problem of the reproductive axis.
What testosterone level counts as low?
The 2026 update to the EAU Guidelines on Sexual and Reproductive Health continues to support a total testosterone threshold of 12 nmol/L (approximately 346 ng/dL) for diagnosing symptomatic hypogonadism, measured on a fasting morning sample. The greatest benefit from treatment is seen in men with more severe deficiency, below 8 nmol/L. It's worth knowing that thresholds vary slightly between guideline bodies — the Endocrine Society uses 264 ng/dL and the American Urological Association uses 300 ng/dL — which is one reason a level must always be interpreted alongside symptoms and repeat testing, not read in isolation.
Do I need more than one blood test to be diagnosed?
Yes. Testosterone should be measured on at least two separate early-morning, fasting blood samples before a diagnosis of hypogonadism is made, because levels fluctuate through the day and a single borderline result can be misleading. Where SHBG (sex hormone-binding globulin) is likely to be abnormal — for example in obesity — a calculated free testosterone is also checked, since total testosterone alone can under- or overestimate the true deficiency.
What causes low testosterone?
Primary hypogonadism results from testicular failure — causes include Klinefelter syndrome, previous chemotherapy or radiotherapy, mumps orchitis, or undescended testes. Secondary hypogonadism results from reduced pituitary or hypothalamic stimulation — causes include pituitary tumours, haemochromatosis, opioid use, and idiopathic hypogonadotropic hypogonadism. A large proportion of cases seen in general and endocrinology practice are functional hypogonadism, where obesity, poorly controlled Type 2 diabetes, chronic illness or significant weight change lower testosterone without a structural cause — and treating the underlying condition is the recommended first step, per the 2026 EAU guidance.
What is testosterone replacement therapy and what does it involve?
Testosterone replacement therapy (TRT) is the treatment of confirmed hypogonadism with exogenous testosterone, usually as a daily transdermal gel (Testogel is HPRA-licensed in Ireland) or a long-acting intramuscular injection (Nebido is HPRA-licensed in Ireland, typically given around every 10–14 weeks once stabilised). The right formulation depends on patient preference, lifestyle and monitoring requirements. TRT can improve energy, mood, libido, erectile function, muscle mass and bone density in men with genuine hypogonadism, but it is not appropriate for men with normal testosterone or for symptoms without biochemical confirmation.
Who should not start testosterone therapy?
Testosterone therapy should not be started in men with untreated prostate or breast cancer, a palpable prostate abnormality or unexplained elevated PSA pending urological assessment, a desire to conceive in the near term (testosterone suppresses natural sperm production), untreated severe obstructive sleep apnoea, uncontrolled heart failure, a myocardial infarction or stroke within the previous six months, thrombophilia, or unexplained elevated haematocrit. Some of these are relative rather than absolute depending on individual circumstances, which is why specialist assessment matters before starting treatment.
Can men with a history of prostate cancer ever have testosterone therapy?
This has traditionally been considered an absolute contraindication, and remains one for untreated or active prostate cancer. However, evidence in men on active surveillance or with a sustained undetectable PSA after definitive treatment has evolved in recent years, and testosterone therapy is now cautiously considered in carefully selected cases. This is a specialist, individualised decision made jointly with urology — not a routine or default approach — and is not something to pursue outside proper multidisciplinary assessment.
What monitoring is needed once treatment starts?
Men on testosterone therapy need baseline PSA testing (from age 40) repeated periodically, along with haematocrit and lipid checks, plus clinical review of symptoms and testosterone levels. Haematocrit above 54% requires stopping or reducing treatment and investigating for contributing causes such as sleep apnoea. Rising PSA — a velocity greater than 0.4 ng/mL per year, an absolute value over 4.0 ng/mL, or a rise of more than 1.4 ng/mL from baseline — prompts urological referral rather than continuing treatment unchecked.
Is low testosterone just a normal part of ageing?
Testosterone does decline gradually with age, by roughly 1–2% per year from the late 30s onward, and this is sometimes called late-onset hypogonadism or andropause. But not all age-related decline needs treatment, and not all low testosterone in an older man is simply ageing — treatable causes such as obesity, sleep apnoea, medication effects or pituitary disease should be actively considered. A specialist assessment distinguishes expected age-related change from a genuine, treatable deficiency.
Can low testosterone affect fertility?
Yes, and this needs to be addressed before starting treatment. Exogenous testosterone suppresses the pituitary signals (LH and FSH) that drive natural sperm production, so standard TRT is not appropriate for men actively trying to conceive. Where fertility is a priority, alternative approaches — such as gonadotropin therapy or referral to a reproductive specialist — are considered instead, and this should always be discussed openly before treatment begins.
References
Primary sources cited in this article, listed in order of appearance.
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1
European Association of Urology. EAU Guidelines on Sexual and Reproductive Health: A Summary of the 2026 Recommendations for Measurement and Biochemical Confirmation of Hypogonadism.
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2
European Association of Urology Guidelines on Male Sexual and Reproductive Health: 2025 Update on Male Hypogonadism, Erectile Dysfunction, Premature Ejaculation, and Peyronie's Disease. European Urology. 2025.
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3
EAU Guidelines on Sexual and Reproductive Health — Male Hypogonadism chapter. Uroweb.
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4
The Endocrine Society. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline.
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5
Health Products Regulatory Authority (Ireland). Testogel 50 mg, transdermal gel in sachet — Summary of Product Characteristics.
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6
Health Products Regulatory Authority (Ireland). Nebido 1000 mg/4 ml solution for injection — Summary of Product Characteristics.
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