Testosterone is a male sex hormone, secreted by Leydig or interstitial cells of the testes, regulated and controlled through negative feedback on the hypothalamus and pituitary gland by the pituitary hormone, luteinizing hormone (LH). Serum concentrations of testosterone will go through a sequence of rise and fall through the fetal stage until 6 months after delivery due to maternal hormonal changes. From 6 months through puberty, testosterone concentration remains at about 1 nmol/L (0.3 ng/mL). The increase of testosterone levels in males is gradual post puberty until it reaches the adult level. In females, testosterone is mainly produced by
peripheral conversion of prehormones.
Testosterone is highly protein-bound. In males, 98% of the testosterone in circulation is bound; the value is slightly lower in females. The majority of the steroid is bound to a specific binding protein, sometimes referred to as Sex Hormone Binding Globulin (SHBG) or Testosterone Binding Globulin (TeBG), and serum
albumin. Testosterone monitoring is used clinically to diagnose and differentiate endocrine disorders. In males, these include hypogonadonism, testicular failure, infertility, hypopituitarism and hyperprolactinemia. In females, polycystic ovary syndrome, adrenal hyperplasia, infertility, hirsutism, amenorrhea, obesity and virilization
can cause changes in serum testosterone levels.
Manufacturer’s Reagent package insert Architect 2nd Generation Testosterone, November 2016, ABBOTT MAX-Planck-Ring 2 65205 Wiesbaden, Germany.