Free Testosterona

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 production. 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.