The Signs of Low Testosterone, and When It Is Actually Worth Testing

The symptom list for low testosterone that circulates online is so long and so vague that it fits almost every man over forty who has had a difficult year. That is not an accident; a broad list sells more products than a narrow one. The clinical literature is much more disciplined, and knowing which symptoms actually carry information will save you either an unnecessary purchase or an unnecessary year of wondering.

The three symptoms that carry signal

When researchers set out to define low testosterone rigorously rather than assume it, they looked for symptoms that correlated with measured hormone levels rather than symptoms men merely reported. The European Male Ageing Study, published as an identification of late-onset hypogonadism in middle-aged and elderly men, found the sexual symptoms did this and the others largely did not. Three stood out: reduced sexual desire, fewer sexual thoughts, and loss of morning erections.

Everything else on the internet’s list — fatigue, low mood, irritability, brain fog, reduced strength, poor sleep — is common in men with low testosterone and equally common in men with normal testosterone who are sleep-deprived, depressed, drinking too much, hypothyroid or simply fifty and stressed. They are worth mentioning to a doctor. They are not evidence of a hormonal problem.

Who is actually worth testing

How the test has to be done

This is where most self-directed testing goes wrong. Testosterone follows a daily rhythm that peaks in the morning, and it falls with acute illness, sleep loss and even recent food. The Endocrine Society’s clinical practice guideline on testosterone therapy in men with hypogonadism therefore requires a morning, fasting total testosterone on a reliable assay, confirmed by a second sample, before any diagnosis is made.

The reason is not bureaucratic. A study of variability in total testosterone levels in ageing men with symptoms of androgen deficiency documented how far the same man’s readings move between draws. A single low result is frequently not reproduced, which means acting on one is a good way to acquire a diagnosis you do not have.

Total, free and SHBG: reading the report

Most testosterone in blood is bound to sex hormone-binding globulin and is not available to tissues; a smaller fraction is loosely bound to albumin, and a small remainder circulates free. A review of the role of SHBG in the free hormone hypothesis and the relevance of free testosterone explains both the model and its limits.

The practical consequence is that SHBG changes the meaning of a total testosterone result. It rises with age and with hyperthyroidism and liver disease; it falls with obesity, insulin resistance and hypothyroidism. So an older, slim man can have a reassuring total with a low free fraction, and a younger man with obesity can have a low total with a less depressed free fraction. This is why free or calculated free testosterone is often measured alongside the total — and why SHBG is the reason ingredients like boron attract interest at all.

What happens after a genuinely low result

A confirmed low testosterone is the beginning of an investigation, not the end of one. A clinical overview of adult male hypogonadism sets out the sequence: repeat the measurement, then check luteinising hormone, follicle-stimulating hormone and prolactin to distinguish a primary testicular problem from a secondary pituitary or hypothalamic one.

Just as important is the search for reversible contributors, because several common ones exist: obesity, untreated obstructive sleep apnoea, opioid analgesics, glucocorticoids, excess alcohol and acute illness. Functional hypogonadism — low testosterone driven by these factors rather than by a fault in the axis — often improves when the cause is addressed, which is a far better outcome than a lifelong prescription.

Common mistakes worth avoiding

Testing in the afternoon. Levels are lower later in the day; an afternoon sample can manufacture a false diagnosis.

Testing during or just after illness. Acute illness lowers testosterone temporarily. Wait until you are well.

Testing at the end of a terrible week. Sleep restriction lowers daytime testosterone measurably within a week, so a bad fortnight can distort the result — see deep sleep and testosterone production.

Comparing laboratories. Assays differ, and so do reference ranges. Use the same laboratory for the repeat.

Treating the number instead of the man. A borderline result with no specific symptoms is usually not a reason to intervene, and a normal result with severe symptoms means the cause is elsewhere — which is the more useful finding.

What the evidence shows, and what it does not

What it shows: sexual symptoms track measured testosterone better than physical or psychological ones; a symptomatic low-testosterone syndrome is uncommon in the general ageing population; single measurements vary enough that two morning samples are required; SHBG substantially changes how a total result should be read; a confirmed low result requires investigation of its cause.

What it does not show: that any symptom list can substitute for a blood test, that a home saliva kit is equivalent to a validated assay, or that supplements correct a diagnosed deficiency. If the number is genuinely low, the honest comparison of your options is in supplements versus TRT, and the context for age-related decline is in andropause and male menopause.

Related reading on male vitality

• Andropause and what male menopause really means
• Supplements versus testosterone replacement therapy
• Boron, SHBG and the free testosterone question
• What morning erections indicate

Frequently asked questions