FREE TESTOSTERONE

Adult Male :

• 8.69 - 54.69 pg/ml

Adult Female :

• 0.29 – 3.18 pg/ml
• Follicular Phase : 0.45 - 3.17 pg/ml
• Luteal Phase : 0.46 - 2.48 pg/ml
• Post menopausal : 0.29 - 1.73 pg/ml

• Testosterone, a C 18 steroid, is the most potent naturally secreted androgen. In normal post pubertal males, testosterone is secreted primarily by the testes with only a small amount derived from peripheral conversion of 4- or 5-androstene-3beta, 17betadione (ASD).
• In adult women, it has been estimated that more than 50 % of serum testosterone is derived from peripheral conversion of ASD secreted by the adrenal glands and ovaries, with the reminder derived from direct secretion of testosterone by these glands.
• In most men and women, >50 % of total circulating testosterone is bound to sex hormone-binding globulin, SHBG, and most of the rest is bound to albumin. SHBG-bound testosterone is not readily available for intracellular complex formation because of SHBG's high binding affinity for testosterone. Thus, testosterone-bound SHBG is considered to be biologically inactive.
• Albumin has a much lower binding affinity for testosterone but binds a significant portion of the total testosterone because albumin is present at much higher plasma concentrations than SHBG. The rapid dissociation of “weakly bound" testosterone from albumin, together with a relatively long transit time of albumin through target tissue capillary beds, result in the availability of essentially all albumin-bound testosterone for steroid-receptor interaction. The sum of the free- and albumin- bound testosterone is often referred to as bioavailable testosterone
• Measurement of the free or unbound fraction of serum testosterone has been proposed as means of estimating the physiologically bioactive hormone
• Free testosterone levels are elevated in women with hyperandrogenism associated with hirsutism in the presence or absence of polycystic ovarian disease. The test is used in evaluation of a case of male infertility, evaluation of a case of hirsutism in females,
  Differential diagnosis of secondary amenorrhoea of females, Diagnosis of testicular feminization syndrome and Evaluation of a case of Polycystic ovarian disease.
• Factors affecting SHBG levels will alter total testosterone levels but free testosterone levels remain unchanged.
• When measuring testosterone levels, it is most important to look at the level of free testosterone, because it is the free testosterone found in blood serum that is the active one

• In men, the test is done when infertility is suspected or when man has decreased sex drive or erectile dysfunction
• When a young boy seems to be undergoing precocious puberty
• In Woman when there is irregular periods or Amenorrhoea, infertility and masculine features 

Males:

• Congenital adrenal hyperplasia
• Adrenal virilizing tumour causing premature puberty in boys
• Testosterone peripheral resistant cases

Females:

• Ovarian stromal hyperthecosis
• Adrenal hyperplasia
• Polycystic ovarian syndrome
• Adrenal virilizing tumour causing masculinization in women

• Primary hypogonadism (eg. Orchiectomy)
• Secondary hypogonadism (eg. Hypopituitarism)
• Testicular feminization
• KIeinfelter's syndrome