- Testosterone (T) is the principal circulating androgen in males. Testosterone deficiency (TD) is characterized by low levels of T in addition to signs and symptoms.
- No universally accepted threshold of T concentration to distinguish eugonadal from hypogonadal men, but the U.S. Food and Drug Administration (FDA) definition is T <300 ng/dL
- T levels correlate with overall health and may be associated with sexual dysfunction.
- Synonym(s): hypogonadism, hypoandrogenism, androgen deficiency, low T
Overall incidence increases with age. T levels decline by 1% per year after the age of 40 years.
- Estimates of TD vary; typically 20% of men >60 years, 30% >70 years, and 50% >80 years of age
- Symptomatic TD in the United States in ages 40 to 69 years is 6–12.3%.
- 2.4 million men in the United States aged 40 to 69 years
Etiology and Pathophysiology
Hypothalamus produces GnRH, which stimulates pituitary to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH). LH stimulates Leydig cells to produce T. Leydig cells are responsible for 90% of the body’s T.
- Primary hypogonadism: Testes produce insufficient amount of T; FSH/LH levels are elevated.
- Secondary hypogonadism: low T from inadequate production of LH
- Congenital syndromes: cryptorchidism, Klinefelter, hypogonadotropic hypogonadism (Kallmann)
- Acquired: cancer, trauma, orchiectomy, steroids
- Infectious: mumps orchitis, HIV, tuberculosis
- Systemic: Cushing syndrome, hemochromatosis, autoimmune, severe illness (e.g., renal and liver disease), metabolic syndrome, obesity, obstructive sleep apnea
- Medications and drugs: LHRH agonists, corticosteroids, ethanol, marijuana, opioids, SSRIs
- Elevated prolactin: prolactinoma, dopamine antagonists (neuroleptics and metoclopramide)
- Klinefelter syndrome: XXY karyotype
- Kallmann syndrome: abnormal GnRH secretion due to abnormal hypothalamic development
- Obesity, diabetes, COPD, depression, thyroid disorders, malnutrition, alcohol, stress
- Chronic infections, inflammatory states, narcotic use
- Undescended testicles, varicocele
- Trauma, cancer, testicular radiation, chemotherapy, disorders of the pituitary and/or hypothalamus
General health maintenance and treatment of obesity
Commonly Associated Conditions
- Infertility, erectile dysfunction, low libido
- Diabetes, insulin resistance, metabolic syndrome, adiposity
- Depressed mood, poor concentration, irritability
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