Low testosterone in men

In shortTestosterone deficiency is not diagnosed from one test: the level is confirmed twice, in the morning, fasting, outside acute illness. Then the report is read as a block: total testosterone with SHBG and the free fraction shows the scale, LH and FSH show the level of failure (testes or brain control), prolactin and estradiol are the frequent hidden causes.

Step one: the correct measurement

Testosterone has a daily rhythm with a morning maximum and reacts to everything: poor sleep, acute illness, alcohol, yesterday's workout. Rule number one is therefore a morning fasting draw in a calm state. Rule number two is confirmation: a single low value proves nothing; it is repeated on another day in the same conditions.

Guidelines on testosterone deficiency in men explicitly require two-fold confirmation of a low level combined with characteristic symptoms: laboratory without clinical picture and clinical picture without laboratory make no diagnosis.

Step two: total, free and SHBG

Total testosterone is the sum of the bound and free fractions. Sex hormone-binding globulin (SHBG) rises with age, in liver disease and with some medications: with high SHBG the total level looks decent while the free, active part is already low. The opposite situation occurs in obesity and insulin resistance, where SHBG is reduced.

In disputed cases, free testosterone is measured or calculated from total and SHBG. Laboratories offer direct measurement and calculated indices; the clinician chooses the method that fits the situation.

Step three: LH, FSH and the level of failure

Luteinizing hormone is the pituitary's control signal to the testes. The pair 'testosterone plus LH' separates two large branches: low testosterone with high LH means the pituitary is shouting while the testes do not answer — primary failure. Low testosterone with low or unraised LH means the command is not arriving — secondary, central failure. FSH complements the picture from the spermatogenesis side.

The further route depends on the fork: the primary branch goes to a urologist-andrologist with testicular assessment, the secondary to a search for causes at the pituitary and hypothalamus level, from medications to prolactinoma.

Step four: prolactin, estradiol and the metabolic background

Elevated prolactin suppresses the control signal and quickly lowers testosterone — one of the reversible causes that must not be missed. Estradiol in men is made from testosterone, and with marked obesity the conversion intensifies: estradiol rises, testosterone falls. Both lines enter the extended block for low testosterone.

A separate layer is the metabolic background: obesity, insulin resistance, sleep apnea and chronic diseases lower testosterone functionally. Guidelines on testosterone deficiency in men with diabetes stress: correcting weight and the metabolic background is part of treatment, not an optional extra.

What distorts a testosterone measurement

An afternoon draw — the level is physiologically lower
Acute illness, sleep deprivation, stress, alcohol the day before
A hard workout within a day of the test
A single measurement without confirmation

Markers covered in this article

Testosterone Free testosterone Sex hormone-binding globulin Luteinizing hormone Prolactin Estradiol

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Frequently asked questions

One test showed low testosterone — is that a diagnosis?

No. The level is confirmed by a repeat morning measurement on another day, and the diagnosis is made only when persistently low values combine with characteristic symptoms. That is what guidelines require.

Why is SHBG drawn with testosterone?

SHBG determines which share of the hormone is free and active. With high SHBG, total testosterone masks low free; with low, the reverse. Without this line the total level is easily misread.

What does the testosterone-LH pair show?

The level of failure: low testosterone with high LH is a testicular problem; with low or normal LH it is the control link (pituitary, hypothalamus). The whole further route depends on this.

What does prolactin have to do with it?

Elevated prolactin suppresses testosterone production — one of the reversible causes. It is included in the block for low testosterone, especially in the secondary branch.

Can weight affect testosterone?

Yes, in two ways: obesity lowers SHBG and intensifies the conversion of testosterone to estradiol. Correcting weight and the metabolic background under medical supervision is a mandatory part of working with low testosterone.

Symptoms are there but testosterone is in range — what then?

The symptoms of deficiency are nonspecific: fatigue and low libido have dozens of causes, from sleep deprivation to depression and sleep apnea. The clinician checks alternatives: TSH, ferritin, glucose, prolactin.

Sources

Testosterone deficiency (hypogonadism) in men with diabetes — clinical guideline context — Minzdrav of Russia (cr.minzdrav.gov.ru). Accessed: August 29, 2026.
Testosterone, Free and Total (test directory, reference intervals) — Labcorp / Esoterix Endocrinology Expected Values. Accessed: August 31, 2026.
SHBG Blood Test: MedlinePlus Medical Test — MedlinePlus, US National Library of Medicine. Accessed: August 31, 2026.

Low testosterone in men: the confirmation sequence from first test to cause