Low testosterone

What low testosterone is

Testosterone is the principal male sex hormone. It is produced in the testicles under instruction from the pituitary gland in the brain, and it governs libido, erectile function, sperm production, muscle and bone mass, red blood cell production, energy and mood.

Male hypogonadism means the testicles are not producing enough of it. Levels fall naturally with age — roughly 1% a year from around 30 — but a genuinely low level at any age is a medical finding that deserves investigating rather than simply replacing.

Symptoms

• Reduced sex drive, and fewer spontaneous or morning erections
• Erectile dysfunction, often alongside other causes rather than instead of them
• Persistent fatigue and reduced stamina
• Low mood, irritability, poor concentration and disturbed sleep
• Loss of muscle bulk and strength, with increased body fat, particularly around the abdomen
• Reduced body and facial hair
• Hot flushes and sweats
• Reduced bone density, and fracture from minor injury
• Small or shrinking testicles, and reduced fertility

None of these is specific to testosterone deficiency. Thyroid disease, depression, sleep apnoea, anaemia, diabetes and simple overwork all produce the same picture, which is exactly why a diagnosis should not rest on symptoms alone.

The two types, and why the distinction matters

• Primary hypogonadism — the testicles themselves are failing. LH and FSH are high because the brain is shouting at testicles that cannot respond. Causes include Klinefelter syndrome, undescended testicles, mumps orchitis, testicular injury or torsion, and previous chemotherapy or radiotherapy.
• Secondary hypogonadism — the testicles are capable, but the signal from the pituitary is inadequate. LH and FSH are low or inappropriately normal. Causes include pituitary tumours, obesity, opioid painkillers, anabolic steroid use, severe illness and, importantly, previously prescribed testosterone.

This distinction changes everything about treatment. Secondary hypogonadism is frequently reversible, and in a man who wants children it can often be treated in a way that raises his own testosterone and preserves sperm production, rather than shutting it down.

How I assess it

Diagnosis requires the right test, taken the right way, confirmed:

• Two morning samples taken before 10am, fasting, on separate days. Testosterone follows a daily rhythm and is at its highest in the morning; an afternoon sample can look falsely low and is a common source of misdiagnosis.
• SHBG and calculated free testosterone, since sex hormone binding globulin changes with age, obesity and thyroid disease and can make a total reading misleading.
• LH, FSH and prolactin, to separate primary from secondary and to detect a pituitary cause.
• Semen analysis, if fertility matters to you now or might later.
• General screening — HbA1c, lipids, thyroid function, full blood count, PSA where appropriate, and vitamin D.
• Pituitary MRI where testosterone is very low, prolactin is raised, or there are visual or headache symptoms.
• Bone density where deficiency has been long-standing.

Treatment

Not every man with a borderline result needs treating, and the first step is often not a prescription at all:

• Treat the cause. Weight loss, treating obstructive sleep apnoea, reviewing opioids and stopping anabolic steroids can restore levels without any replacement at all. In obesity in particular, the gains can be substantial.
• Testosterone replacement — gels, long or short-acting injections, or implants — where deficiency is confirmed, symptomatic and family plans allow. Requires monitoring of levels, haematocrit and PSA.
• Fertility-sparing treatment. In secondary hypogonadism, medications that stimulate your own production can raise testosterone while maintaining sperm production. This is the right route for most men who still want children, and it is under-offered.
• Sperm storage before starting replacement, as insurance, where plans may change.

Why see an andrologist for this

Low testosterone sits precisely at the junction of hormones, sexual function and fertility — the three things my practice is built around. Men are frequently either dismissed with a normal-range result that was taken at 4pm, or started on lifelong replacement without anyone asking whether they want more children. Both are avoidable. I look after this alongside erectile dysfunction and male infertility, so the treatment plan accounts for all three at once.