Testosterone is hormone produced by the adrenal glands and gonads. Its concentration in the blood can vary considerably depending on the lifestyle, diet, age, climatic conditions of residence, heredity and even the time of day. But its concentration is always in men ten times higher than in women.Testosterone belongs to the group of androgens ─ male hormone responsible for the development of secondary sex traits. The progress of the majority of physiological processes as manly appearance and sexual activity directly dependent on its concentration. Good physical condition, excellent memory and attention, energy and men natural behavior is sign of adequate secretions produced by glands.Normally, this androgen is able to protect the psyche from stress, normalize metabolic processes, to prevent the development of atherosclerosis, hypertension and other cardiovascular pathologies. The deficiency, as well as excess of this hormone dramatically affects the aspect and behavior of both men and women.Testosterone levels: norm and deviationsTo determine the level of testosterone in the body is needed blood tests. Doctors assess its concentration studying two key indicators: total and free. Norm of total androgen levels in the blood for men is considered 2,6-11,0 ng/ml; in females ─ 0,26-1,30 ng/ml. About 2% is in pure form, the remaining is bound with proteins. Biologically is active both bound and free hormone.