Total Testosterone

Aka: Total Testosterone, Serum Testosterone, Testosterone Level, Serum Total Testosterone, Testosterone

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II. Physiology

  1. Androgenic steroid synthesized in males, in the leydig cells of the Testis
  2. Release is stimulated by Luteinizing Hormone release from the Pituitary Gland
    1. In a negative feedback loop, Testosterone suppresses release of LF and FSH from the pituitary
  3. Mechanism
    1. Activity via Testosterone, or by its conversion to dihydrotestosterone (DHT) irreversibly by 5-alpha reductase
  4. Responsible for male sex characteristics and male reproductive function
    1. Facial hair
    2. Deep voice
    3. Muscle growth
    4. Spermatogenesis
    5. Libido

III. Pathophysiology

  1. Low Levels
    1. See Male Hypogonadism
    2. See Androgen Decline in the Aging Male
  2. Elevated Levels
    1. See Precocious Puberty
    2. See Anabolic Steroid

IV. Technique

  1. Obtain in the morning (or within 2 hours of awakening) due to circadian variation

V. Labs: Interpretation

  1. Normal Levels
    1. Male: 300 to 1000 ng/100 ml
    2. Female: <70 ng/100 ml

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