Testosterone in the blood

Testosterone is an androgen hormone responsible for secondary sexual characteristics in men. The most important source of testosterone is the Leydig cells of the testes. Testosterone supports spermatogenesis, stimulates the growth and functioning of the accessory sex glands, and the development of the penis and scrotum. The hormone has an anabolic effect, mainly on bones and muscles. Due to its direct effect on the bone marrow, as well as by activating the synthesis of erythropoietin in the kidneys, testosterone stimulates erythropoiesis. The hormone is also necessary for maintaining libido and potency. Testosterone synthesis is controlled by LH of the anterior pituitary gland. In men, it is the main androgen that causes the achievement of sexual maturity. The concentration of the hormone in the blood increases after physical exertion. The reference values of testosterone concentration in the blood serum are given in the table.

In healthy adult men, the peak concentration of testosterone occurs in the morning and decreases by at least 25% in the evening. After 50 years, a progressive decrease in testosterone levels in the blood is observed.

Serum testosterone concentrations increase in idiopathic precocious puberty and adrenal cortex hyperplasia in boys, adrenal cortex tumors, extragonadal tumors in men, trophoblastic diseases in pregnant women, and arrhenoblastomas.

A decrease in the concentration of testosterone in the blood is observed in Down syndrome and delayed puberty.

Reference values (norm) of testosterone concentration in blood serum

Age	Floor	Testosterone
		Ng/dl	Nmol/l
Newborns	Male	75-400	2.6-13.9
	Female	20-64	0.69-2.22
Prepubertal age:
1-5 months	Male	1-177	0.03-6.14
	Female	1-5	0.03-0.17
6-11 months	Male	2-7	0.07-0.24
	Female	2-5	0.07-0.17
1-5 years	Male	2-25	0.07-0.87
	Female	2-10	0.07-0.35
6-9 years	Male	3-30	0.10-1.04
	Female	2-20	0.07-0.69
Puberty age:
1 age group	Male	2-23	0.07-0.80
	Female	2-10	0.07-0.35
2 age group	Male	5-70	0.17-2.43
	Female	5-30	0.17-1.04
3 age group	Male	15-280	0.52-9.72
	Female	10-30	0.35-1.04
4 age group	Male	105-545	3.64-18.91
	Female	15-40	0.52-1.39
5 age group	Male	265-800	9.19-27.76
	Female	10-40	0.35-1.39
Adults	Male	280-1100	8.72-38.17
	Female	15-70	0.52-2.43
Pregnant women	3-4 times higher than normal concentration
Postmenopause		8-35	0.28-1.22

Approximately 2% of testosterone circulating in the blood is in a free state. Only free testosterone is able to penetrate the cell, bind to intracellular receptors, penetrate the nucleus and change gene transcription (that is, ultimately realize its biological effects).

Reference values (norm) of free testosterone concentration in blood serum

	Floor	Free testosterone
Age		Pg/ml	Pmol/l
Newborns	Male	1.5-31	5.2-107.5
	Female	0.5-2.5	1.7-8.7
1-3 months	Male	3.3-8	11.5-62.7
	Female	0.1-1.3	0.3-4.5
3-5 months	Male	0.7-14	2.4-48.6
	Female	0.3-1.1	1.0-3.8
5-7 months	Male	0.4-4.8	1.4-16.6
	Female	0.2-0.6	0.7-2.1
Children:
6-9 years	Male	0.1-3.2	0.3-11.1
	Female	0.1-0.9	0.3-3.1
10-11 years	Male	0.6-5.7	2.1-9.8
	Female	1.0-5.2	3.5-18
12-14 years old	Male	1.4-156	4.9-541
	Female	1.0-5.2	3.5-18
15-17 years old	Male	80-159	278-552
	Female	1-5.2	3.5-18
Adults	Male	50-210	174-729
	Female	1.0-8.5	3.5-29.5

Free testosterone is independent of the SHBG concentration. Therefore, free testosterone determination is indicated in situations where the SHBG content may increase ( hyperthyroidism, hyperestrogenism, pregnancy, taking oral contraceptives or antiepileptic drugs) or decrease (hypothyroidism, obesity ).