Background: The testes secrete two different hormones into the blood stream, inhibin and testosterone and both hormone productions are regulated by feedback mechanisms with the pituitary hormones, FSH and LH respectively. Both FSH and LH (through production of testosterone) are necessary for stimulation of normal spermatogenesis. In addition, testosterone has specific effects through receptors in many parts of the body, which it reaches through the blood stream. The major fraction of testosterone in blood is bound to a carrier protein and only the free testosterone fraction is bioactive. The testosterone concentration in blood varies throughout the 24 hours and must be measured at known times to be estimated as normal. The testosterone concentration in blood is highest around 8 am, following an increase in stimulation by LH around 5 am.
Symptoms: Testosterone production by the testes is necessary for normal spermatogenesis. Testosterone is necessary for development of normal puberty. It has a stimulatory role in muscle function, bone structure, blood production and male pattern of hair growth. Testosterone has some effect on vitality, libido, and erectile function. Decline of these functions may be symptoms of low testosterone production, although they are also greatly affected by mental status. Testosterone production is maintained throughout life but is reduced with age. The age at which testosterone in blood falls below the concentration seen in younger men varies from individual to individual and may be late in life. Sperm production, however, is not changed significantly by age.
Diagnosis: Diagnosis of low testosterone production is made by measurement of LH, FSH, and testosterone in blood. The bioactive free testosterone concentration may be low even with a normal total testosterone concentration, but in that case LH and FSH concentrations will be relatively increased. Clinical symptoms play important roles in the diagnosis of low testosterone production, but some are difficult to evaluate because of the interference by an individual’s mental status. Genetic abnormalities are the most common cause of primary low testosterone production.
Treatment: Testosterone treatment is used in people with documented abnormal low testosterone production and a reactive increase in FSH and LH concentrations in blood. Testosterone treatment requires regular control of prostate and coronary status because of possible adverse effects of high doses of testosterone on prostate size, prostate cancer, coronary atherosclerosis, and red blood cell proliferation. Testosterone may be administered by injection or by application of skin cream (which circumvent first passage through the liver) or by oral tablets (which are absorbed in a first passage through the liver). It is not used for supplementary treatment of fatigue, low vitality, low erectile function, or low muscle strength in men with normal concentrations of testosterone and normal concentrations of LH and FSH in blood. Nor is it used as a “trial” treatment for these symptoms in men with normal testosterone production. Testosterone treatment is part of gender change of females to males (FTM).
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