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For IN VITRO determination of Free Testosterone (FT) levels
in hirsutism and hypogonadism.
Free testosterone diffuses through cell membranes and binds to specific receptor
proteins (androgen receptors); the Testosterone-receptor complexes act as
transcriptional modulators on cis-regulatory regions of many genes.
Excess of Androgens in women causes hirsutism and signs of virilization;
Testosterone level in serum has to be determined before and after ovarian and
adrenal stimulation and supression to identify the source of excessive hormone
Primary and secondary hypogonadism in men result in clinical hypoandrogenization,
correlated with the degree of gonadal failure in Testosterone production. The
determination of serum Testosterone together with that of LH allows the correct
assessement of those conditions.
The diagnosis of true anorchia also requires to discriminate this condition from
cryptorchidism. Under prolonged hCG stimulation, Testosterone levels remain very
low in true anorchia while cryptorchid testes can respond to stimulation.
Androgen resistance syndromes, due to X linked androgen receptor gene
deficiencies, are made of various degrees of sexual ambiguity. Whatever the
severity of the phenotypical abnormalities, serum Testosterone is systematically high
in regards to elevated LH serum levels in these conditions.
Testosterone assays include total testosterone (direct, extraction, coated tubes) and
free testosterone determinations.
Total Testosterone in plasma includes free Testosterone and Testosterone bound to
SHBG, albumin, CBG. The mean percentage of each in normal men is 2.7, 32, 65
and <0.1 respectively.
Solvents break the protein binding in extraction assays whereas blocking agents
release Testosterone from proteins in direct assays. The advantage of a free
testosterone assay is that free testosterone concentrations are in equilibrium with
testosterone bound to receptors in the organs.