Residency · Residency · Endocrinology

Male Hypogonadism

Classification

Primary Hypogonadism (Hypergonadotropic)

Primary hypogonadism results from testicular failure, producing low testosterone with elevated LH and FSH as the pituitary attempts to compensate for inadequate gonadal function. Klinefelter syndrome (47,XXY), the most common genetic cause occurring in 1 in 600 males, presents with tall stature, small firm testes (typically less than 6 mL), gynecomastia, sparse body hair, and infertility (azoospermia). These patients face increased risk of metabolic syndrome, breast cancer, and autoimmune disease, and diagnosis is confirmed by karyotype. Cryptorchidism (undescended testes) carries risks of both infertility and testicular cancer, even after surgical orchidopexy. Orchitis, particularly bilateral mumps orchitis occurring in 15-30% of post-pubertal cases, can cause significant testicular damage. Testicular torsion, when bilateral or treated with delayed surgical correction, leads to primary gonadal failure. Radiation and chemotherapy produce dose-dependent gonadotoxicity, with alkylating agents such as cyclophosphamide being the most gonadotoxic; germ cells are more sensitive than Leydig cells, and sperm banking before treatment is recommended. Additional causes include trauma, surgery, anorchia (vanishing testes syndrome), myotonic dystrophy (progressive testicular failure), and rare genetic causes including DAX1 mutations, SF-1 mutations, and LH or FSH receptor mutations.

Secondary Hypogonadism (Hypogonadotropic)

Secondary hypogonadism results from hypothalamic or pituitary failure, producing low testosterone with low or inappropriately normal LH and FSH. Congenital forms include Kallmann syndrome, caused by failure of GnRH neuron migration during embryonic development. Multiple genes have been implicated, including KAL1 (X-linked), FGFR1, PROKR2, and PROK2. The hallmark is anosmia or hyposmia combined with hypogonadism, along with potential midline defects (cleft palate), renal agenesis, and hearing loss. MRI characteristically demonstrates absent or hypoplastic olfactory bulbs. Idiopathic hypogonadotropic hypogonadism (IHH) presents similarly but without anosmia and involves various GnRH pathway mutations (KISS1R, TAC3, TACR3, GnRHR). Constitutional delay of puberty, a normal variant featuring delayed but eventually complete puberty with a positive family history, can be difficult to distinguish from IHH in adolescence.

Acquired causes of secondary hypogonadism are numerous and clinically important. Pituitary tumors, with prolactinoma being the most common cause of acquired secondary hypogonadism in men, suppress gonadotropin secretion. Hyperprolactinemia from any cause suppresses GnRH pulsatility. Pituitary surgery, radiation, apoplexy, and infiltrative disease can damage gonadotroph function. Obesity is a particularly prevalent cause: increased aromatization of testosterone to estradiol in adipose tissue, combined with estradiol-mediated suppression of LH, produces functionally low testosterone that often normalizes with weight loss. Opioid-induced hypogonadism occurs in 40-80% of men on chronic opioid therapy in a dose-dependent fashion and is often reversible with opioid reduction or cessation. Anabolic steroid abuse causes profound suppression of LH and FSH through exogenous androgen feedback, leading to testicular atrophy and azoospermia; recovery may take months to years after cessation, and some men never recover. Critical illness, sleep deprivation, excessive exercise, and eating disorders can all transiently suppress the hypothalamic-pituitary-gonadal axis. Hemochromatosis causes iron deposition in pituitary gonadotrophs and is the most common endocrine manifestation of the disease. Late-onset hypogonadism reflects the gradual decline in testosterone of approximately 1-2% per year after age 30, resulting from multifactorial pituitary and testicular components and associated with obesity and metabolic syndrome.

Combined primary and secondary hypogonadism may be seen with aging, chronic illness, HIV, alcohol use disorder, and sickle cell disease.

<image>A diagnostic classification diagram for male hypogonadism. Divide into two main columns: Primary (Hypergonadotropic) and Secondary (Hypogonadotropic). For each column, list congenital and acquired causes. Primary congenital: Klinefelter (show karyotype 47,XXY), cryptorchidism, anorchia. Primary acquired: orchitis, torsion, radiation/chemotherapy, trauma. Secondary congenital: Kallmann (show absent olfactory bulbs on MRI), IHH, constitutional delay. Secondary acquired: prolactinoma, obesity, opioids, anabolic steroids, hemochromatosis, pituitary surgery/radiation. In the center, show the HPG axis with hypothalamus (GnRH), pituitary (LH/FSH), and testes (testosterone, sperm), with indicators of where each category disrupts the axis. Include laboratory patterns: Primary = low T, high LH/FSH; Secondary = low T, low/normal LH/FSH. Use educational diagram style.</image>

Diagnosis

When to Test

Testing for hypogonadism should be considered in men presenting with decreased libido, erectile dysfunction, fatigue, depressed mood, loss of body hair, decreased muscle mass, gynecomastia, infertility, decreased bone density, or small testes. High-risk populations warranting screening include men with type 2 diabetes (prevalence 25-40%), metabolic syndrome, obesity, chronic opioid use, HIV, prior chemotherapy or radiation, pituitary disease, Klinefelter syndrome, and chronic glucocorticoid use.

Biochemical Diagnosis

Total testosterone must be measured in the morning before 10:00 AM, preferably fasting (as food and glucose suppress testosterone levels), using a reliable assay with liquid chromatography-tandem mass spectrometry (LC-MS/MS) preferred over immunoassay. A level below 300 ng/dL (10.4 nmol/L) is considered low per the Endocrine Society, though some authorities use 264 ng/dL based on Framingham data for young men. At least two low morning testosterone measurements on separate days are required for diagnosis.

Free testosterone should be assessed when total testosterone is borderline (200-400 ng/dL) and conditions that alter SHBG are present. Calculated free testosterone using the Vermeulen formula is preferred over direct immunoassay, which is inaccurate. Low free testosterone is generally defined as below 5-9 ng/dL depending on assay and population. SHBG elevation (from aging, hyperthyroidism, liver disease, anticonvulsants, HIV, or estrogen) increases total testosterone without increasing bioavailable testosterone. SHBG suppression (from obesity, diabetes, hypothyroidism, nephrotic syndrome, androgens, or glucocorticoids) decreases total testosterone while free testosterone may be preserved.

Additional Workup

LH and FSH levels distinguish primary hypogonadism (elevated) from secondary (low or inappropriately normal). Prolactin should be measured when secondary hypogonadism is identified, to exclude prolactinoma. Iron studies and ferritin screen for hemochromatosis in secondary hypogonadism. Pituitary MRI is indicated when secondary hypogonadism is confirmed, particularly with elevated prolactin or other pituitary hormone deficiencies. Karyotype should be obtained when primary hypogonadism presents with small testes in a young male to screen for Klinefelter syndrome. Semen analysis should be performed at a specialized laboratory after 2-5 days of abstinence when fertility is a concern. Baseline CBC (for polycythemia risk assessment), lipid panel, HbA1c, PSA (before initiating TRT), and DXA (when osteoporosis is suspected) complete the evaluation.

Late-Onset Hypogonadism (LOH)

Late-onset hypogonadism reflects the age-related decline in testosterone and affects a variable proportion of aging men depending on how strictly it is defined. The European Male Aging Study (EMAS) found that only 2% of men aged 40-79 met strict criteria requiring both low total testosterone and three sexual symptoms. The critical distinction is between organic hypogonadism and functional hypogonadism related to obesity or illness, the latter of which responds to weight loss and management of the underlying condition. Testosterone replacement in LOH remains more controversial than in clear organic hypogonadism.

Treatment

Testosterone Replacement Therapy (TRT)

Formulations

Topical gels (1%, 1.62%, or 2% formulations such as AndroGel, Testim, and Vogelxo) are applied at 20.25-81 mg daily to the shoulders, upper arms, or abdomen. They achieve steady state in 1-3 days but carry a risk of transdermal transfer to women and children, requiring application to skin that will be covered and careful hand washing. Topical solution (Axiron) is applied to the axillae at 30-120 mg daily. Transdermal patches (Androderm) deliver 2-6 mg daily applied to the torso but are limited by skin irritation in approximately 30% of users.

Intramuscular injections include testosterone cypionate or enanthate at 100-200 mg every 1-2 weeks (or 50-100 mg weekly for more stable levels), which offer the most cost-effective option but produce peak-trough variability. Testosterone undecanoate (Aveed) provides long-acting coverage at 750 mg intramuscularly with loading doses at weeks 0 and 4, then every 10 weeks, delivering more stable levels. It requires a REMS program due to rare pulmonary oil microembolism risk, with administration in a clinical setting and 30-minute post-injection observation.

Nasal gel (Natesto) at 5.5 mg per nostril three times daily is short-acting and may preserve spermatogenesis due to lower gonadotropin suppression, though the dosing schedule is inconvenient. Subcutaneous pellets (Testopel) at 150-450 mg are implanted every 3-6 months through a minor procedure, providing consistent levels with risk of extrusion. Oral testosterone undecanoate (Jatenzo/Tlando) at 158-396 mg twice daily with food requires lymphatic absorption and avoids the first-pass metabolism that makes older oral formulations like methyltestosterone hepatotoxic and contraindicated.

Monitoring on TRT

Testosterone levels should be checked at 3 months, measured as a mid-injection trough for IM preparations or 2-8 hours after application for gels, targeting 400-700 ng/dL at trough. Hematocrit and hemoglobin should be assessed at baseline, 3-6 months, and then annually, as testosterone stimulates erythropoiesis. If hematocrit exceeds 54%, the dose should be reduced, therapy held, and phlebotomy considered due to the risk of thromboembolic events. PSA and digital rectal exam should be performed at baseline and 3-6 months, then per standard cancer screening guidelines; while testosterone does not cause prostate cancer, it may stimulate growth of pre-existing occult disease. Urology referral is indicated when PSA increases more than 1.4 ng/mL in 12 months or exceeds 4.0 ng/mL absolute. Lipid monitoring (HDL may decrease slightly), liver function testing (only needed for oral formulations), DXA at 1-2 years if baseline osteoporosis is present, and symptom assessment using validated questionnaires complete the monitoring framework.

Contraindications to TRT

Contraindications include desire for current fertility (TRT suppresses spermatogenesis), male breast cancer, untreated prostate cancer (though TRT may be cautiously considered in select patients after definitive treatment with undetectable PSA based on emerging data), baseline hematocrit above 50% (relative contraindication), untreated severe obstructive sleep apnea, severe heart failure (NYHA class IV, though the TRAVERSE trial provides reassurance), and thrombophilia.

Cardiovascular Safety of TRT

Historical concerns about cardiovascular safety based on observational studies and a 2015 FDA warning have been substantially addressed. The TRAVERSE trial (2023), a randomized, placebo-controlled trial of testosterone gel in men aged 45 and older with cardiovascular disease or risk factors and documented hypogonadism, demonstrated non-inferiority for the primary MACE endpoint (HR 0.96) with no increased cardiovascular risk, leading to an FDA label update. However, TRAVERSE did identify small absolute increases in atrial fibrillation, acute kidney injury, and pulmonary embolism.

Fertility Preservation

TRT suppresses spermatogenesis through negative feedback on GnRH, LH, and FSH, resulting in testicular atrophy and azoospermia in 40-60% of men within 3-6 months. For men desiring current or future fertility, TRT should not be initiated, and alternative approaches should be employed.

Clomiphene citrate, used off-label at 25-50 mg orally daily or on alternate days, is a selective estrogen receptor modulator that blocks estrogen negative feedback, increasing LH and FSH and thereby raising testosterone while maintaining spermatogenesis. It typically raises testosterone by 200-300 ng/dL without causing testicular atrophy and is first-line for secondary hypogonadism when fertility is desired. Enclomiphene, the trans-isomer of clomiphene and a more selective estrogen receptor antagonist, is in clinical development.

Human chorionic gonadotropin (hCG) at 1500-3000 IU subcutaneously 2-3 times weekly acts as an LH analog, stimulating Leydig cells to produce testosterone while maintaining intratesticular testosterone and spermatogenesis. It can be used alone or in combination with TRT, though it is expensive. For men with secondary hypogonadism who fail to develop sperm on hCG alone, recombinant FSH or hMG at 75-150 IU subcutaneously 3 times weekly is added, as FSH is needed for spermatogenesis initiation. Pulsatile GnRH pump therapy, delivering 5-25 mcg every 120 minutes, is the most physiologic approach for hypothalamic causes but has limited availability.

Recovery of spermatogenesis after TRT discontinuation occurs in most men, with 90% recovering by 12 months. However, some may have permanent impairment, particularly after prolonged anabolic steroid abuse.

<image>A treatment decision flowchart for male hypogonadism. Start with confirmed hypogonadism (low morning testosterone x2 + symptoms). First decision: Does patient desire current/future fertility? If YES → clomiphene citrate 25-50 mg daily (secondary hypogonadism) or hCG 1500-3000 IU SC 2-3x/week (± FSH if needed). If NO → testosterone replacement therapy (TRT). TRT branch: choose formulation based on patient preference (show options: topical gel daily, IM injection q1-2 weeks, IM undecanoate q10 weeks, nasal TID, pellets q3-6 months, oral BID). Monitoring panel: testosterone level at 3 months, hematocrit at 3 and 6 months then annually, PSA at baseline and 3-6 months, symptoms. Red flag boxes: stop/reduce if hematocrit >54%, PSA rise >1.4 in 12 months, severe symptoms. Include contraindications checklist before starting TRT.</image>

Specific Clinical Scenarios

Obesity-Related Hypogonadism

Low total testosterone is found in 25-50% of obese men, though only 10-15% have low free testosterone. The mechanism involves increased aromatization by adipose CYP19, SHBG suppression, hypothalamic dysfunction, and sleep apnea. Weight loss through bariatric surgery, GLP-1 receptor agonists, or lifestyle modification significantly increases testosterone and often normalizes it. TRT in obese men provides modest body composition benefits but does not substitute for weight management. The Endocrine Society recommends pursuing weight loss first before diagnosing organic hypogonadism in obese men, recognizing that much of the testosterone deficiency is functional.

Anabolic Steroid Abuse

An estimated 1-3 million men in the US have used anabolic steroids. Exogenous androgens profoundly suppress LH and FSH, producing testicular atrophy (often below 8 mL) and azoospermia with infertility. After discontinuation, recovery takes 3-12 months or longer, and hCG and clomiphene citrate can assist the process. Some men never recover, particularly after prolonged use at high doses, and may require long-term TRT. Additional complications include polycythemia, cardiomyopathy, hepatotoxicity (with oral androgens), and psychiatric effects.

Klinefelter Syndrome Management

TRT should be initiated at the expected age of puberty (11-12 years) when testosterone is low and continued lifelong. Fertility, once considered impossible, can now be achieved through micro-TESE (testicular sperm extraction) in 30-50% of cases for use with IVF/ICSI. Monitoring should address the increased risk of metabolic syndrome, type 2 diabetes (prevalence 10-40%), breast cancer (20-fold increased risk), osteoporosis, and autoimmune disorders (SLE, thyroid disease). Psychological support addresses the increased risk of anxiety, depression, and learning difficulties.

Key Clinical Pearls

• Always measure morning (before 10 AM) fasting total testosterone and confirm with a second measurement on a separate day before diagnosing hypogonadism; a single low value is insufficient
• Obesity is the most common cause of low total testosterone in men; much of this is functional (increased aromatization, decreased SHBG); weight loss of 10-15% can normalize testosterone without TRT
• TRT suppresses spermatogenesis and can cause infertility; in men who desire current or future fertility, clomiphene citrate or hCG are fertility-preserving alternatives that raise testosterone while maintaining spermatogenesis
• The TRAVERSE trial established cardiovascular safety of testosterone in hypogonadal men with CV risk factors; TRT is not contraindicated with cardiovascular disease per current evidence, but monitor hematocrit closely (>54% requires dose reduction)
• In secondary hypogonadism, always check prolactin and consider pituitary MRI; prolactinoma is the most common pituitary cause of acquired hypogonadotropic hypogonadism in men
• Chronic opioid use causes hypogonadism in 40-80% of men; this is often overlooked; testosterone levels should be checked in all men on chronic opioids with symptoms of hypogonadism

References

1. Bhasin S, et al. "Testosterone Therapy in Men with Hypogonadism: An Endocrine Society Clinical Practice Guideline." J Clin Endocrinol Metab. 2018;103(5):1715-1744.
2. Lincoff AM, et al. "Cardiovascular Safety of Testosterone-Replacement Therapy (TRAVERSE)." N Engl J Med. 2023;389(2):107-117.
3. Corona G, et al. "European Academy of Andrology (EAA) Guidelines on Investigation, Treatment and Monitoring of Functional Hypogonadism in Males." Andrology. 2020;8(5):970-987.
4. Rastrelli G, et al. "Testosterone Replacement Therapy for Sexual Symptoms." Sex Med Rev. 2019;7(3):464-475.
5. Dwyer AA, et al. "Hypogonadotropic Hypogonadism." Curr Opin Endocrinol Diabetes Obes. 2019;26(6):301-309.

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