Testosterone deficiency — hypogonadism — is a genuine clinical condition. It has a definition, a diagnostic pathway and an established treatment. It is also the condition most likely to be self-diagnosed from a symptom list on a forum, because its symptoms are so general that almost any tired, low, out-of-shape man will recognise himself in them.
Both things are true at once, and holding them together is the whole difficulty. Some men genuinely have it and go years without being taken seriously. Others are convinced they have it, have a normal result, and are sold something anyway. Understanding what the diagnosis actually requires protects you from both outcomes.
What the symptoms are
The British Society for Sexual Medicine groups the symptoms into sexual, physical and psychological. The sexual symptoms carry the most diagnostic weight, because they are the least explainable by everything else going on in a person's life.
- Sexual — reduced libido, fewer spontaneous morning erections, erectile difficulty, reduced ejaculate volume
- Physical — loss of muscle mass and strength, increased body fat especially around the middle, reduced body hair, hot flushes, low bone density
- Psychological — persistent low mood, irritability, poor concentration, low motivation, disturbed sleep, fatigue that rest does not fix
The physical and psychological symptoms on that list are shared with underactive thyroid, iron deficiency, depression, obstructive sleep apnoea, chronic stress and simply being under-slept. That overlap is why symptoms alone cannot make the diagnosis, and why a good assessment always looks wider than testosterone.
The two kinds of deficiency
This distinction matters more than the testosterone number itself, because it determines what is actually wrong and what should be done about it.
| Primary (testicular) | Secondary (pituitary or hypothalamic) | |
|---|---|---|
| What has failed | The testes themselves | The signal telling the testes to work |
| Testosterone | Low | Low |
| LH and FSH | High — the brain is shouting | Low or inappropriately normal — the brain is quiet |
| Common causes | Klinefelter's, mumps orchitis, trauma, chemotherapy, undescended testes | Obesity, opioids, anabolic steroid use, pituitary tumour, severe illness, sleep apnoea |
| Why it matters | Rarely reversible; treatment is usually replacement | Often reversible — treat the cause and testosterone can recover |
Where the thresholds sit
UK practice broadly follows the BSSM guidance. Diagnosis requires consistent symptoms plus two separate morning blood samples taken on different days — never a single reading.
| Total testosterone | Interpretation |
|---|---|
| Below 8 nmol/L | Deficiency likely. Treatment usually considered if symptoms fit. |
| 8–12 nmol/L | The grey zone. Free testosterone and SHBG are needed; a trial of treatment may be considered where symptoms are convincing. |
| Above 12 nmol/L | Deficiency unlikely to be the explanation. Look elsewhere. |
Those numbers are guides, not verdicts. A man at 11 nmol/L with high SHBG may have less usable testosterone than a man at 9 nmol/L with low SHBG, because SHBG binds testosterone and holds it out of circulation. This is why a total testosterone result on its own answers very little.
Getting a result that means something
- Sample before 10am. Testosterone follows a daily rhythm and reference ranges are built on morning samples.
- Do not test during or shortly after an acute illness. Testosterone drops transiently and the result will mislead.
- Measure SHBG and albumin alongside, so free testosterone can be calculated.
- Measure LH and FSH, which separate primary from secondary.
- Repeat any abnormal result on a second day before drawing conclusions.
If your results suggest deficiency, the next step is a GP appointment, not a purchase. Ask for the abnormal result to be repeated, for LH, FSH and prolactin if they were not done, and for the reversible causes to be considered before anything is started.
Sources
BSSM guidelines on adult testosterone deficiency, 2022
Diagnostic thresholds, the requirement for two morning samples, and the role of free testosterone in the 8–12 nmol/L range.
NICE Clinical Knowledge Summary: Hypogonadism
Primary care assessment, differential diagnosis and referral criteria.
European Academy of Andrology guidelines
Classification of primary and secondary hypogonadism and the reversibility of functional causes.