Hypogonadism in Men: Diagnosis, Thresholds, and When to Treat

Hypogonadism is defined as failure of the testes to produce sufficient testosterone, sperm, or both. The clinical syndrome requires both biochemical confirmation (low serum testosterone) and symptoms attributable to androgen deficiency — neither alone is sufficient for diagnosis or treatment initiation. Understanding the diagnostic framework avoids both undertreatment of genuine deficiency and overtreatment of men with low-normal testosterone who are symptomatic for other reasons.

Prevalence

Symptomatic hypogonadism affects an estimated 2–6% of men overall, rising to 20–30% in men over 60. The Hypogonadism in Males (HIM) study screened men over 45 and found 38.7% had total testosterone below 300 ng/dL, though not all were symptomatic. [^mulligan2006] The prevalence of biochemically confirmed, symptomatic hypogonadism requiring treatment is substantially lower — approximately 5–10% in men over 50.

Classification

Primary Hypogonadism (Hypergonadotropic)

Primary hypogonadism originates in the testes — the gonads fail to produce adequate testosterone. The pituitary responds by increasing LH and FSH secretion (hence "hypergonadotropic"). LH and FSH are elevated or high-normal; testosterone is low.

Causes:

• Klinefelter syndrome (47,XXY) — the most common genetic cause, affecting 1 in 650 men
• Bilateral orchidectomy or testicular atrophy from trauma, torsion, or infection
• Chemotherapy or radiation damage to testicular tissue
• Mumps orchitis (uncommon with widespread vaccination)
• Anorchia (congenital absence of testes)
• Autoimmune orchitis

Primary hypogonadism is irreversible in most cases. Treatment is testosterone replacement therapy; fertility is generally impaired and requires specialized reproductive assistance.

Secondary Hypogonadism (Hypogonadotropic)

Secondary hypogonadism originates at the hypothalamus or pituitary — inadequate GnRH or LH/FSH secretion fails to stimulate the testes. LH and FSH are low or inappropriately normal; testosterone is low. The testes are functional if adequately stimulated.

Causes:

• Functional: Obesity (most common reversible cause — adipose tissue aromatizes testosterone to estradiol, suppressing LH via negative feedback), sleep apnea, opioid use, anabolic steroid use (exogenous androgens suppress endogenous LH/FSH)
• Structural pituitary: Pituitary adenoma (prolactinoma most commonly), hemochromatosis, pituitary surgery or radiation
• Hypothalamic: Kallmann syndrome (GnRH deficiency with anosmia), idiopathic hypogonadotropic hypogonadism
• Systemic illness: HIV, chronic kidney disease, liver cirrhosis, uncontrolled diabetes

Secondary hypogonadism from reversible causes (obesity, opioids, sleep apnea) can normalize with treatment of the underlying condition — addressing these before initiating TRT is essential. [^dandona2010]

Late-Onset Hypogonadism (Age-Related)

Age-related testosterone decline (approximately 1–2% per year after age 40) produces a mixed picture: some men develop primarily secondary hypogonadism (declining LH pulse amplitude with age) while others show primary testicular decline. The term "late-onset hypogonadism" describes this syndrome without implying a single mechanism.

Symptoms

No symptom is pathognomonic for hypogonadism, but the most specific ones are:

High specificity (more likely to reflect androgen deficiency):

• Reduced morning erections
• Reduced sexual thoughts and fantasy
• Erectile dysfunction (particularly loss of desire component)
• Incomplete development of secondary sexual characteristics (if onset in adolescence)
• Reduced testicular volume

Moderate specificity:

• Decreased libido
• Loss of body/facial hair
• Hot flushes, sweating
• Gynecomastia (breast enlargement/tenderness)

Low specificity (common in hypogonadism but also in many other conditions):

• Fatigue and low energy
• Depressed mood
• Reduced concentration
• Decreased muscle mass, increased fat mass
• Decreased bone density

The Endocrine Society guidelines emphasize that treatment should be reserved for men with both low testosterone AND symptoms — not asymptomatic low testosterone alone, and not symptomatic men with normal testosterone. [^bhasin2010]

Symptom questionnaires (ADAM, AMS, IIEF) are screening tools, not diagnostic instruments. A positive questionnaire in a man with normal testosterone does not establish hypogonadism.

Diagnostic Criteria

Step 1: Serum Total Testosterone

Total testosterone should be measured in the morning (7–11 AM) when diurnal peak occurs. Testosterone is 15–30% higher in morning samples than afternoon — afternoon low-normal values may be within range by morning. [^bhasin2010]

The Endocrine Society defines hypogonadism as total testosterone below 300 ng/dL (10.4 nmol/L) on two separate morning measurements on different days. The two-sample requirement filters out day-to-day biological variation — a single low value can be spurious.

Important caveat: Total testosterone binds to sex hormone-binding globulin (SHBG) and albumin. Only free testosterone (~2–3% of total) and loosely albumin-bound testosterone are biologically active. Men with high SHBG (obesity, liver disease, aging) have lower free T for a given total T; men with low SHBG (obesity, insulin resistance, hypothyroidism) may have normal free T despite low total T.

Step 2: Free or Bioavailable Testosterone

When total testosterone is borderline (300–400 ng/dL) or SHBG levels are suspected to be abnormal, free testosterone should be measured. The equilibrium dialysis method is most accurate; calculated free T (using total T and SHBG with the Vermeulen formula) is acceptable if dialysis is unavailable.

Free testosterone below 65 pg/mL (225 pmol/L) is generally considered low by most guidelines, though reference ranges vary by laboratory. [^morales2010]

Step 3: LH and FSH

Once low testosterone is confirmed, LH and FSH distinguish primary from secondary:

Step 4: Additional Workup

For secondary hypogonadism (low LH/FSH):

• Prolactin — elevated prolactin suppresses GnRH/LH; pituitary adenoma must be excluded
• MRI pituitary — if prolactin is elevated or very low testosterone with very low LH suggests structural lesion
• Iron/ferritin — hemochromatosis is a reversible cause of secondary hypogonadism
• Opioid and anabolic steroid history

For all patients:

• SHBG (if total T borderline)
• CBC — baseline hematocrit before treatment
• PSA — baseline before TRT in men over 40 (TRT can stimulate prostate growth)
• Metabolic workup — glucose, lipids, HbA1c (hypogonadism is associated with metabolic syndrome)

For primary hypogonadism:

• Karyotype (if azoospermia or markedly elevated FSH) to identify Klinefelter
• Semen analysis if fertility desired

Thresholds in Context

The 300 ng/dL threshold is a pragmatic cutoff, not a physiological absolute. Zitzmann et al. (2006) showed that symptoms begin appearing below 400 ng/dL for libido and sexual function, and below 300 ng/dL for more severe symptoms. The relationship between testosterone level and symptoms is continuous rather than binary, with substantial inter-individual variation. [^zitzmann2006]

Some men with total testosterone of 280 ng/dL are highly symptomatic; others with 290 ng/dL are asymptomatic. Conversely, some men with 350 ng/dL have genuine symptoms from relatively low free T due to high SHBG.

Clinical judgment must integrate the laboratory result with symptom burden, free T if indicated, and exclusion of other causes for the symptoms before recommending treatment.

Conditions That Mimic Hypogonadism

The non-specific symptoms of hypogonadism (fatigue, mood change, reduced concentration, weight gain) overlap extensively with:

• Depression and anxiety disorders
• Sleep disorders (especially obstructive sleep apnea — which also causes secondary hypogonadism)
• Hypothyroidism
• Anemia
• Chronic disease (kidney, liver, cardiovascular)
• Opioid use disorder
• Type 2 diabetes

These must be evaluated and treated before attributing symptoms to testosterone deficiency — and several (sleep apnea, obesity, opioids) are themselves causes of secondary hypogonadism that may normalize testosterone when addressed. [^buvat2013]

Absolute Contraindications to TRT

• Prostate cancer (androgen-sensitive — TRT may stimulate growth)
• Breast cancer (rare in men, androgen-sensitive)
• Polycythemia vera (TRT stimulates erythropoiesis, worsening hematocrit)
• Untreated severe obstructive sleep apnea (TRT may worsen airway tone)
• Active desire for fertility (TRT suppresses spermatogenesis; alternative: clomiphene citrate or hCG stimulation preserves fertility while raising testosterone)
• Recent MI or stroke (<6 months — based on caution pending TRAVERSE-level data for this subgroup)

Monitoring After Treatment Initiation

If TRT is initiated, monitoring is required: [^rhoden2004]

• Testosterone: Recheck at 3–6 months, targeting mid-normal range (400–700 ng/dL)
• Hematocrit: Baseline, 3–6 months, then annually — dose-reduce if >54%
• PSA: Baseline, 3–6 months, then annually — significant rise warrants urology referral
• Symptom assessment: Formal re-evaluation at 3–6 months to confirm response

Bottom Line

Hypogonadism diagnosis requires two confirmed morning total testosterone readings below 300 ng/dL plus attributable symptoms — neither criterion alone justifies treatment. LH/FSH distinguish primary (testicular failure, high gonadotropins) from secondary (hypothalamic-pituitary failure, low/normal gonadotropins). Secondary hypogonadism from reversible causes — obesity, sleep apnea, opioids — should be addressed before initiating TRT. Free testosterone clarifies borderline total T values, particularly in men with abnormal SHBG. Symptom overlap with depression, hypothyroidism, and sleep disorders requires systematic exclusion before attributing complaints to androgen deficiency.