Testosterone

• Testosterone

  • Principal androgen in the blood
  • Most potent made androgen
  • Secretion is controlled by Luteinizing Hormone (LH)
  • 5% free, unbound protein
• C-19 steroid hormone mainly synthesized by Leydig cell of the testis

  • Also derived from progesterone
• Functions of Testosterone

  Growth & development of:

  • Reproductive system
  • Prostate 
  • External genitalia
• Method used for Testosterone

  Immunoassay
• • Testosterone is also present in females (vice versa)
  • Produced by adrenal glands
• Factors affecting Testosterone

  • Exhibit circadian rhythm
  • Peak - time of awakening (8am)

  Lowest lvl - 8pm
• > 30 yrs old:

  • Gradual reduction
  • Average decline:
  •  110 ng/dL per decade
• MEN >50 yo:

  Experience decrease in secretion rate & concentration of testosterone
• WOMEN >50 yo:

  • Experience increase in pituitary gonadotropins, esp follicle stimulating hormone (FSH)
• What happens to testosterone if a person is obese?

  Can cause decrease in plasma testosterone concentration
• Transport Proteins of testosterone

  • Albumin - 50%
  • Sex Hormone-Binding Globulin - 45%

  (During lab estimation, the concentration of binding proteins determines the of total testosterone but NOT the free testosterone)
• LAboratory Test for Testosterone: Automated Immunoassay

  • Fastest method for assessing testosterone levels 
  • Most commonly used method
  • Used to assess men w/ suspected hypogonadism / testosterone deficiency
  • Measures free, albumin bound, SHBG-bound testosterone in the blood
  • Time of Blood Collection: 7am-10am
• Free Testosterone

  • Measures only 2% of total testosterone
  • Method: Direct immunoassay test kit
  • Easiest and Fastest available method of assessing free testosterone
  • Testosterone Abs & Tracer particles which bind to free testosterone in the sample

  Results are less accurate than other methods