The pituitary exclusion before TRT commencement is the most important safety step in testosterone deficiency management — secondary hypogonadism (low testosterone from pituitary/hypothalamic failure) can be caused by a prolactinoma, a non-functioning pituitary adenoma, a craniopharyngioma, or hypopituitarism from other causes. The key investigation is a serum prolactin alongside LH and FSH. Elevated prolactin + low LH/FSH + low testosterone = prolactinoma until proven otherwise → MRI pituitary urgently. Treating a prolactinoma with TRT alone (without cabergoline) will not restore testicular function, will not shrink the tumour, and may allow the tumour to grow undetected. Cabergoline treatment alone for a prolactinoma typically normalises testosterone in 60–70% of men within 3–6 months. The TRT and fertility issue is one of the most important counselling points in younger men — testosterone replacement therapy causes iatrogenic infertility through suppression of FSH (needed for spermatogenesis) and LH (needed for intratesticular testosterone production). This is potentially irreversible if TRT is taken for prolonged periods (testicular atrophy). The recovery of spermatogenesis after stopping TRT may take 6–24 months and is not guaranteed. Any man who may wish to have biological children must be counselled specifically about this before starting TRT, and alternatives (hCG, clomiphene) discussed. This conversation must be documented.

The requirement for two separate morning testosterone measurements is fundamental to the diagnosis — testosterone levels have a diurnal rhythm with peak levels in the morning (7–9 AM) and trough levels in the afternoon/evening (up to 35% lower). A single low testosterone measured at 2 PM may simply reflect normal diurnal variation rather than true deficiency. BSSM (British Society for Sexual Medicine) and EAU (European Association of Urology) guidelines both specify that at least two early morning fasting testosterone measurements must be below the reference range on separate occasions (typically 4–12 weeks apart) before TRT is initiated. This prevents treatment of transient testosterone suppression from acute illness, stress, obesity, or alcohol. The differential diagnosis of testosterone deficiency symptoms is the reason a structured approach matters — a middle-aged man presenting with fatigue, low mood, low libido, and weight gain could have hypothyroidism, type 2 diabetes, depression, obstructive sleep apnoea, or anaemia — all of which must be excluded first, as they are more common than true hypogonadism, and treating them addresses the root cause without the risks and commitments of TRT.

The LH/FSH result is the critical branch point in testosterone deficiency — elevated LH/FSH with low testosterone confirms primary (testicular) hypogonadism, which requires TRT but NOT pituitary investigation. Low or inappropriately normal LH/FSH with low testosterone confirms secondary (central) hypogonadism, which requires MRI pituitary to exclude a structural cause before TRT is commenced. This distinction cannot be made from testosterone alone. Functional hypogonadism from obesity is one of the most clinically important and actionable diagnoses — severely obese men (BMI >40) frequently have total testosterone levels in the hypogonadal range due to increased aromatisation of testosterone to oestradiol in adipose tissue and increased SHBG binding. These men should be managed with weight loss first — bariatric surgery in morbidly obese men with functional hypogonadism routinely normalises testosterone to eugonadal levels without TRT. Starting TRT in a functionally hypogonadal obese man without addressing obesity means continuous treatment dependency, suppression of the HPG axis, and testicular atrophy — whereas weight loss is potentially curative. Opioid-induced hypogonadism is under-recognised and affects approximately 70% of men on long-term opioids for chronic pain — opioids suppress GnRH pulsatility, reducing LH/FSH and thus testosterone production. Any man on long-term opioids presenting with TD symptoms should have his opioid regimen reviewed as a priority — dose reduction, opioid rotation, or switch to buprenorphine (which causes less HPG axis suppression) may restore testosterone without TRT.

The SHBG (sex hormone-binding globulin) calculation of free testosterone is clinically important in borderline cases — total testosterone can be misleadingly low in men with low SHBG (obesity, diabetes, hypothyroidism, nephrotic syndrome) because a higher fraction is free and bioavailable, even though the total looks low. Conversely, total testosterone can be misleadingly normal in men with very high SHBG (ageing, liver disease, hyperthyroidism) while the bioavailable fraction is actually deficient. The Vermeulen formula (freely available online) calculates free testosterone from total testosterone + SHBG + albumin and is the standard method used in BSSM and EAU guidelines to assess bioavailable testosterone in borderline cases. The PSA baseline before TRT is a clinical governance and medicolegal imperative — TRT is absolutely contraindicated in prostate cancer, and an elevated PSA before starting TRT both identifies men who need prostate cancer exclusion and provides the baseline from which PSA monitoring on TRT is interpreted. A rapid rise in PSA after starting TRT (PSA velocity >1 ng/ml/year or 0.4 ng/ml rise in 6 months) is an indication for urgent urology referral. The PSA discussion must be documented as an informed consent conversation — "we need to check your PSA before starting testosterone to make sure there is no prostate cancer, and we will monitor it after treatment." Haemochromatosis as a cause of secondary hypogonadism is under-recognised — iron deposition in the anterior pituitary impairs gonadotrophin secretion, causing hypogonadotropic hypogonadism in the presence of iron overload. In a man with low LH/FSH, low testosterone, liver disease, diabetes, arthropathy, and bronze skin → check ferritin and transferrin saturation urgently.

NHS England and BSSM guidelines have shifted significantly toward GP-led TRT initiation in straightforward primary hypogonadism — the intention is to reduce specialist waiting times and provide men with more accessible treatment. However, the prerequisite is that the GP has performed the full diagnostic workup (two morning testosterone levels, LH/FSH, prolactin, SHBG, PSA, FBC, DRE, TSH) and confirmed primary hypogonadism with no contraindications before initiating. Secondary hypogonadism (low LH/FSH) always requires specialist assessment first. The key principle is that GPs should follow their local commissioned pathway — in many NHS trusts there is now a GP TRT pathway with specific investigation requirements, formulary-approved preparations, and monitoring protocols. hCG (human chorionic gonadotrophin) for fertility preservation in hypogonadal men works by acting as an LH analogue — it stimulates the Leydig cells directly to produce intratesticular testosterone, which is required in much higher concentrations than serum testosterone for spermatogenesis to occur. Intratesticular testosterone is approximately 50–100 times higher than serum testosterone. TRT raises serum testosterone but actually reduces intratesticular testosterone (by suppressing LH) — hence the paradox that TRT causes azoospermia despite restoring serum testosterone to normal. hCG bypasses this by directly stimulating the testes without suppressing the pituitary.

Transdermal testosterone gel is the preferred first-line preparation because it provides stable daily testosterone levels (mimicking normal physiological diurnal rhythm) rather than the supraphysiological peaks and subphysiological troughs of fortnightly injections. The principal safety concern with transdermal gel is transfer to female partners and children — testosterone exposure in women can cause virilisation (acne, hair growth, clitoral enlargement) and in prepubertal children can cause precocious puberty. The prevention message (dry before contact, cover with clothing, hand-washing) must be explicitly provided at prescription and documented. The pulmonary oil microembolism (POME) risk with Nebido (testosterone undecanoate in castor oil) is rare but real — the castor oil vehicle can form small oil microemboli in the pulmonary vasculature during injection, causing coughing, dyspnoea, chest tightness, and rarely anaphylaxis. This typically occurs during or within minutes of the injection. NHS England guidance recommends a 30-minute observation period post-injection and that the first injection is given in a healthcare setting rather than self-administered. The target testosterone range on TRT (15–30 nmol/L for gel, trough 12–15 nmol/L for injections) ensures adequate replacement without supraphysiological levels that increase polycythaemia, aggression, cardiovascular, and sleep apnoea risks.

The PSA monitoring protocol on TRT is important and must be communicated clearly to patients — the concern is not that TRT causes prostate cancer, but that it can stimulate pre-existing occult prostate cancer cells that were previously quiescent in a low-testosterone environment. The landmark studies (including the testosterone trials in older men) have not shown an increased risk of prostate cancer diagnosis with TRT, but PSA monitoring remains standard of care. The PSA velocity thresholds (0.4 ng/ml rise in 6 months, 1.4 ng/ml rise in 12 months) are more sensitive for prostate cancer detection than the absolute PSA level in men on TRT, because TRT can cause a modest PSA rise that is considered acceptable (up to 1.4 ng/ml in 12 months) — but a rapid rise suggests stimulation of occult cancer. These thresholds are from the BSSM guidelines. Polycythaemia from TRT is the most common significant adverse effect — testosterone stimulates erythropoietin production, which increases red cell mass. The clinical risk is venous and arterial thrombosis (DVT, PE, MI, stroke) from increased blood viscosity. The haematocrit threshold of 0.54 (equivalent to approximately Hb 18 g/dL) is the standard intervention threshold. Injectable testosterone preparations cause higher peak levels and therefore greater erythropoietic stimulation — men on injections have higher rates of polycythaemia than those on gels. Switching to gel or reducing injection frequency/dose often resolves the problem without stopping TRT entirely.

The evidence for lifestyle optimisation before TRT in functional hypogonadism is compelling — a 2019 meta-analysis showed that intensive lifestyle intervention (diet + exercise) in obese men raised testosterone by an average of 2.9 nmol/L, equivalent to the lower end of TRT dose titration. In men with borderline testosterone (8–12 nmol/L) and functional risk factors, a structured 3-month lifestyle programme before TRT reassessment is both evidence-based and clinically responsible — it avoids lifelong TRT in men who can achieve eugonadal testosterone with lifestyle changes, prevents the fertility-suppressing effect of TRT in younger men, and addresses the underlying metabolic risk. The sleep-testosterone relationship is one of the most underappreciated in primary care — multiple studies have shown that chronically short sleep (<6 hours) reduces testosterone by 10–15% within 1 week, and this is reversible with sleep restoration. OSA is particularly important because it is highly prevalent in the obese, middle-aged male TD population, is potentially curable with CPAP/weight loss, and causes significant testosterone suppression through sleep fragmentation and intermittent hypoxia. Every man presenting with TD symptoms and snoring/witnessed apnoea should have OSA formally assessed before TRT is prescribed.

The annual formal review of TRT is a clinical governance requirement — TRT is a long-term commitment with significant implications (polycythaemia risk, prostate surveillance, HPG axis suppression, fertility loss) and must not be continued on an automatic repeat prescription basis. Each annual review should address: ongoing indication (are testosterone levels still deficient? Is there symptomatic benefit? Has an underlying reversible cause been corrected?), side effects and monitoring results, and patient preferences (including fertility plans if applicable). The DXA scan surveillance for bone density in hypogonadism is important — testosterone is a key regulator of bone density in men, and longstanding untreated hypogonadism causes osteoporosis with fragility fracture risk comparable to that seen in post-menopausal women. All men with confirmed hypogonadism should have a baseline DXA scan and repeat scanning every 2 years, with osteoporosis treated per NICE guidelines (calcium + vitamin D + bisphosphonate if T-score <-2.5). The cardiovascular safety of TRT remains an area of ongoing research — the TRAVERSE trial (2023, NEJM) showed no significant increase in major cardiovascular events with TRT in men with hypogonadism and high cardiovascular risk, providing reassurance for prescribing in this population. However, the polycythaemia side effect remains a genuine cardiovascular risk that requires active monitoring.