What is Low Testosterone (Low T)?
 

Low testosterone, medically called hypogonadism, is a clinical syndrome resulting from failure of the testes to produce adequate levels of testosterone and/or normal sperm production, due to dysfunction at one or more levels of the hypothalamic-pituitary-testicular (HPT) axis.
 

The American Urological Association (AUA) uses three principles for diagnosing testosterone deficiency (hypogonadism):
 

1. The Biochemical Cutoff: The AUA recommends using a total serum testosterone level below 300 ng/dL as a standard diagnostic threshold.

2. Repeat Testing Requirement: Because testosterone levels fluctuate and exhibit diurnal variation, guidelines mandate that a diagnosis should never be made off a single lab value. It requires two separate morning blood draws (typically between 8:00 AM and 11:00 AM) that both come back low.

3. Consistent clinical signs or symptoms

   • Sexual Symptoms: Decreased libido, erectile dysfunction, reduced frequency of morning erections, and diminished ejaculate volume.

   • Physical & Somatic Symptoms: Reduced muscle mass and strength, increased visceral body fat, gynecomastia, decreased body/facial hair growth, hot flashes, and reduced bone mineral density (osteopenia or osteoporosis leading to fractures).

   • Cognitive & Mood Symptoms: Fatigue, low energy, depressed mood, irritability, concentration difficulties, and sleep disturbances.

Primary Causes of Low Testosterone
 

• Definition: Testicular failure characterized by low testosterone, elevated luteinizing hormone (LH), and elevated follicle-stimulating hormone (FSH).

• Genetic Conditions: Klinefelter syndrome (XXY karyotype), Y-chromosome microdeletions, and myotonic dystrophy.

• Acquired Testicular Damage: Cryptorchidism (undescended testicles), testicular trauma, orchitis (e.g., mumps), testicular torsion, prior chemotherapy, radiation therapy to the testes

• Aging

Secondary Causes of Low Testosterone
 

• Definition: Central axis failure characterized by low or inappropriately normal testosterone paired with low or low-normal LH and FSH.

• Hypothalamic & Pituitary Tumors: Pituitary adenomas (prolactinomas or non-functioning macroadenomas), craniopharyngiomas, and subsequent mass effect or surgical/radiation damage.

• Infiltrative & Inflammatory Diseases: Hemochromatosis (iron overload in the pituitary), sarcoidosis, histiocytosis, and hypophysitis.

• Systemic & Lifestyle: Severe obesity, diabetes mellitus, chronic systemic illness, chronic kidney or liver disease, obstructive sleep apnea (OSA), COPD, and substance use.

• Genetic Syndromes: Kallmann syndrome (isolated GnRH deficiency with anosmia) and congenital hypopituitarism.

Diagnostics
 

• History & Physical Examination

• Total Serum Testosterone: Must be drawn in the morning. Must be confirmed with a repeat morning test on a separate day if borderline or low. 

• Free or Bioavailable Testosterone: Measured via equilibrium dialysis or calculated when alterations in Sex Hormone-Binding Globulin (SHBG) are suspected (e.g., obesity, aging, liver disease, borderline total testosterone).

• LH and FSH: To differentiate primary (high) from secondary (low/normal) hypogonadism.

• Serum Prolactin: To rule out a prolactin-secreting pituitary adenoma if secondary hypogonadism is identified.

• Iron Panel and Ferritin: To screen for hemochromatosis as a secondary cause of pituitary iron overload.

• Estradiol Sensitive (LC-MS/MS)

• Additional Laboratory Screening: Complete blood count (baseline hematocrit/hemoglobin), lipid panel, comprehensive metabolic panel, and HbA1c.

Management 
 

Non-Pharmacological Management
 

• Lifestyle Modification & Weight Loss: Significant weight loss, structured aerobic and resistance exercise, and management of metabolic syndrome to naturally improve testosterone levels in secondary, obesity-related hypogonadism.

• Treatment of Underlying Conditions: Optimizing glycemic control, addressing nutritional deficiencies, treating obstructive sleep apnea (CPAP therapy), and discontinuing/changing medications (e.g., chronic opioids).

Pharmacological Management
 

• Testosterone Replacement Therapy (TRT):​ Transdermal gels or patches, intramuscular or subcutaneous injections, buccal, oral, or long-acting pellets.

• Secondary Hypogonadism:

  • Human Chorionic Gonadotropin (hCG) injections with or without testosterone replacement therapy to stimulate natural testosterone production and preserve sperm production, testicular function, and testicle size. It has a high cost, requires frequent injections, and increased probability of excess estrogen. 

• Monitoring Protocol: testosterone levels, PSA (prostate-specific antigen), and complete blood count (monitoring for secondary erythrocytosis/elevated hematocrit).

• Aromatase inhibitors (anastrozole), usually as a last resort, if unable to control excessive estrogen with dosing (lowering dose, increasing TRT frequency) and medication changes.