Low testosterone (hypogonadism): the symptoms that actually matter and when to worry

Tiredness, less drive, poorer concentration, the feeling of having lost your spark. It is easy to read a list like that and think of low testosterone. And it is just as easy to find someone willing to sell you that idea, because it fits almost everything. The problem is that real hypogonadism, the clinical syndrome, is not that: it is a very specific combination of symptoms plus a confirmed blood test, and it affects far fewer men than the marketing suggests. Let's separate what the evidence actually says from what has become a catch-all label.

What hypogonadism is and why it happens

Male hypogonadism is a clinical syndrome caused by a deficiency of testosterone (or of sperm). The key word is syndrome: it is not just a number on a blood test, but the combination of compatible signs and symptoms alongside persistently low blood testosterone concentrations. Without both together, there is no diagnosis.

Two broad types are distinguished, depending on where the hormonal axis fails. In primary hypogonadism the problem lies in the testis itself, and the pituitary, sensing the lack of testosterone, drives the gonadotrophins up: LH and FSH come back high. In secondary or central hypogonadism the fault is higher up, in the hypothalamus or the pituitary, and those same gonadotrophins come back low or inappropriately normal. This distinction is not a technicality: it points to the cause and shapes management.

There is also an important difference between organic hypogonadism, caused by a structural problem of the axis, and functional hypogonadism, which is reversible and usually down to obesity, illness or certain medicines. In the functional form, the reasonable first line is often not lifelong testosterone but treating the underlying cause. In fact, much of the fall in testosterone attributed to age is explained more by the comorbidities that build up over the years (obesity, diabetes, poor general health) than by age itself. And obesity is a key factor and, what's more, potentially reversible with weight loss.

Which symptoms really matter

This is the nuance almost nobody mentions. In the European Male Ageing Study (EMAS), the large European study on this subject involving 3,369 men from eight centres (one of them in Santiago de Compostela), the symptoms most closely associated with genuinely low testosterone were the sexual ones, and quite specifically: reduced libido and fewer sexual thoughts, weaker morning erections and erectile dysfunction. When all three appear together, they are the strongest predictor.

The rest of the symptoms we tend to link to low testosterone (fatigue, loss of strength, low mood, difficulty concentrating) are non-specific. It is not that they don't count, it is that they overlap with plenty of other things: depression, sleep apnoea, anaemia, hypothyroidism, or simply sleeping badly or going through a rough patch. Putting isolated tiredness, with no sexual symptoms at all, down to testosterone is precisely the most common mistake.

How it is diagnosed (and why one blood test isn't enough)

The diagnosis requires two things at once: compatible symptoms or signs AND a low total testosterone, unequivocally confirmed. And confirmed means something specific. The initial test is total testosterone measured fasting and in the morning, when levels are highest, and it must be repeated on a different day to confirm that the low value is consistent. A single low reading, and even less so one from an afternoon sample, neither diagnoses anything nor justifies treatment.

Nor is there a single universal threshold, and it is wise to be sceptical of anyone presenting one as absolute truth. The guidelines differ. The Endocrine Society puts the lower limit at around 264 ng/dL (about 9.2 nmol/L) in healthy, non-obese young men. The European urology guidelines (EAU) use 12 nmol/L (about 350 ng/dL) as a reliable threshold for diagnosis, and note that the benefit of treatment is greater when testosterone is below 8 nmol/L. The American urological guideline (AUA) uses below 300 ng/dL (about 10.4 nmol/L). Values also depend on the laboratory and the method used, so interpretation has to be clinical, not automatic.

There is one technical detail that makes all the difference. When total testosterone falls close to the lower limit, or when there are situations that alter SHBG (the protein that transports testosterone) such as obesity, older age, diabetes or thyroid disease, free testosterone needs to be measured or estimated. And not by any old method: by equilibrium dialysis or using a validated formula, never by direct immunoassay, which is unreliable. For reference, the EMAS criterion for late-onset hypogonadism required all three sexual symptoms together with a total testosterone below 11 nmol/L and a free testosterone below 220 pmol/L (a total testosterone below 8 nmol/L was sufficient on its own).

How common it really is

This is where expectations need grounding. In EMAS, the prevalence of symptomatic late-onset hypogonadism, defined by symptoms plus biochemistry, in the general population of men over 40 was just 2.1%. It does rise with age: from 0.1% between 40 and 49, to 0.6% between 50 and 59, 3.2% between 60 and 69 and 5.1% between 70 and 79. These figures are a long way from the widespread notion that a large share of middle-aged and older men have it.

What the evidence says about treatment

When the diagnosis is properly made, testosterone treatment does have effects, but they need to be kept in proportion. The Testosterone Trials, a set of trials in 790 men aged 65 or over with testosterone below 275 ng/dL, compared testosterone gel for a year against placebo. The result: a moderate improvement in sexual function, correction of anaemia (haemoglobin improved) and slight improvements in mood and bone density, but no benefit in vitality or walking distance. Cognitive function did not improve, and an increase in non-calcified coronary plaque volume was seen, whose clinical significance is uncertain.

On cardiovascular safety, the large trial is TRAVERSE: 5,246 men aged 45 to 80 with cardiovascular risk or disease and testosterone below 300 ng/dL. Testosterone proved non-inferior to placebo for major adverse cardiovascular events (7.0% versus 7.3%; HR 0.96). It is important to read that correctly: it demonstrates safety in that respect, not benefit. It is not a reason to prescribe testosterone widely to older men, and in that same study there were more cases of atrial fibrillation, pulmonary embolism and acute kidney injury in the testosterone group. Nor is the treatment free of risks: it can raise the haematocrit, worsen sleep apnoea and suppress sperm production, which is why it is not an option for anyone trying to conceive, and it is contraindicated in active prostate or breast cancer.

Common myths, debunked

• Low testosterone does not equal needing treatment. Without symptoms and without confirmation on two separate days, an isolated low reading neither diagnoses anything nor justifies treatment.
• It is not the andropause or the male menopause. These are imprecise popular terms; the fall in testosterone is gradual, not an abrupt cessation comparable to the menopause, and the scientific societies talk about late-onset hypogonadism.
• It is not as common as it seems. The real prevalence, defined by symptoms plus blood tests, is around 2.1% in men over 40.
• Tiredness or low mood on their own do not point to testosterone. They are non-specific symptoms that share causes with depression, sleep apnoea, anaemia or hypothyroidism.
• Testosterone does not improve memory or cognition: the Testosterone Trials found no cognitive benefit.
• It is not a rejuvenator and it does not protect the heart. TRAVERSE showed safety (non-inferiority), not cardiovascular benefit.
• It is not free of risks and it is not for everyone: it can raise the haematocrit, worsen sleep apnoea and cause infertility, and it is contraindicated in men seeking fertility or with active prostate or breast cancer.

The situation in Spain

In Spain, the AEMPS has authorised several testosterone products for replacement therapy in male hypogonadism confirmed both clinically and by blood tests. These include transdermal gels (such as Testogel or Testavan), long-acting testosterone undecanoate injections (Reandron or Testosterona SIT) and older injectable preparations (Testex Prolongatum). What matters, beyond the brand names, is what the Spanish summary of product characteristics says: use is restricted to deficiency confirmed by clinical and laboratory data, not for normal ageing or for non-specific malaise without a diagnosis. There have also been documented supply problems with some preparations. Since the authorisation and supply status of each brand can change, it is worth checking again at the time on the CIMA website (cima.aemps.es); we don't go into regimens or doses here, because that is an individual clinical decision.

In short, and what to do about it

Real hypogonadism does exist and can be treated when it is properly diagnosed, but it is neither as common as we are told nor something you can settle by interpreting a single blood test. If you recognise yourself above all in the sexual symptoms and you are also dragging around tiredness or low mood, it makes sense to look into it properly: repeated morning blood tests and ruling out common causes such as obesity, sleep apnoea or a thyroid problem.

That assessment is precisely the first step, and it is best taken with medical judgement rather than on the strength of a stray figure or an online quiz. In Spain there is now male hormonal health treatment with a prior assessment, a prescription from a registered doctor when appropriate and ongoing follow-up. If you want to start there, you can check whether you are eligible.