Clinical Information

Testosterone is regarded as the most important of the androgen steroids. In males, it is secreted by the Leydig and interstitial cells of the testes which are stimulated by luteinizing hormone (LH). Control of testosterone secretion is via negative feedback loop to the hypothalamus, whereby secretion of gonadotrophin-releasing hormone promotes synthesis and release of LH and follicle-stimulating hormone (FSH) from the anterior pituitary gland.

In females, testosterone is secreted by the follicular theca and interstitial cells of the ovaries and also produced by metabolism of adrenal androgens. Concentrations are typically about 10-20 times lower for females than for males. In circulation, approximately 97% of testosterone is transported by proteins, most notably bound to sex hormone-binding globulin (SHBG). Testosterone is also weakly bound to albumin.

The concentration of testosterone in an individual fluctuates over 24 hours. The pulsatile release of LH in the night typically leads to a peak of testosterone concentration in the morning. Time of day, age, sex, puberty, pre- and post-menopause, and disease, all have an influence on testosterone concentration and should be considered in interpreting individual results.

The Alinity i 2nd Generation Testosterone assay releases testosterone from binding proteins and measures total testosterone. The assay is to be used for the measurement of testosterone in the diagnosis and treatment of disorders involving the male sex hormones (androgens), including primary and secondary hypogonadism, delayed or precocious puberty, impotence in males and, in females, hirsutism (excessive hair) and virilization (masculinization) due to tumors, polycystic ovaries, and adrenogenital syndromes.