Low testosterone means a blood test has produced a result below the expected range. It is not the same as hypogonadism, which is a clinical diagnosis. Diagnosis requires compatible symptoms, low testosterone confirmed on a second morning test and an assessment of the cause.
How is low testosterone different from hypogonadism?
A low result is a laboratory number. Hypogonadism is a clinical diagnosis: the testes are producing less testosterone than the body needs and this is causing symptoms or signs.
Testosterone changes through the day. It can also fall temporarily during acute illness, with poor sleep, substantial calorie restriction, obesity or certain medicines. That is why one blood test is usually not enough.
The clinician is asking two questions: is the testosterone genuinely and repeatedly low, and does that deficiency explain the clinical picture? If either part is missing, the diagnosis is less secure.
Source: EAU 2026.
What testosterone level is considered low?
There is no single number that works for every man. Each laboratory has a reference range that depends on its method.
The European Association of Urology uses 12 nmol/L, about 346 ng/dL, as a practical threshold in late-onset hypogonadism. It is a reference point, not an automatic dividing line. Near the threshold, SHBG and calculated free testosterone may help.
If a result is low, it is normally repeated in the morning, fasting when possible and when you are clinically well. Timing, recent illness and the timing of a TRT dose can change interpretation. If your result uses different units, use the testosterone converter.
What are total testosterone, SHBG and free testosterone?
Total testosterone is the usual starting test. It measures testosterone that is protein-bound as well as the small fraction circulating freely.
SHBG is the main binding protein for testosterone. It can be high or low because of age, obesity, liver disease, thyroid disease and other factors. When SHBG is abnormal, total testosterone can give an incomplete picture and calculated free testosterone may be useful.
Laboratories do not all measure or calculate free testosterone in the same way, so one universal free-testosterone cut-off should not be applied mechanically.
What types of hypogonadism are there?
Where the problem originates affects the next investigations and treatment. LH and FSH help orientate this because they are pituitary hormones that stimulate the testes.
| Type | What happens | Typical pattern |
|---|---|---|
| Primary | The main problem is in the testes. | Low testosterone with relatively high LH and FSH. |
| Secondary | The hypothalamus or pituitary is providing insufficient stimulation. | Low testosterone with low, or inappropriately normal, LH and FSH. |
| Functional | Another condition suppresses the axis without necessarily causing structural damage. | Can occur with obesity, systemic illness or some medicines. |
These patterns guide investigation but do not replace a full clinical assessment.
What happens after a low result?
Repeat the test
This confirms that the reduction persists rather than being a one-off fluctuation.
Review symptoms and context
Sexual desire, erections, strength, sleep, medicines, weight, fertility plans and testicular or pituitary history.
Find the cause
LH, FSH, SHBG and other investigations are selected according to the clinical pattern.
Decide whether treatment is appropriate
Not every man with one low number needs TRT. Some causes are reversible and others need a different treatment.
When should you seek medical advice promptly?
Seek prompt medical assessment if low testosterone occurs with a new severe headache, visual changes, nipple discharge, a significant testicular change or signs of another systemic illness. A specific cause may need investigation rather than treating this as simple "low testosterone".