Laboratory determination of the hormone testosterone in the blood, the main androgen in men in terms of importance, in many diseases has not only significant diagnostic and prognostic value, but also therapeutic and prophylactic.
The hormone is synthesized from cholesterol and acetic acid. In men, it is produced in the testicles by Leydig cells (95-98%) and, in small amounts, in the adrenal cortex (3-5%). Testosterone is also partly produced by regional metabolism. Its almost complete destruction and conversion to 17-ketosteroids occurs in the liver and partly in tissues.
Testosterone fractions and their normal values
In the blood, the hormone circulates in three forms or fractions:
- Strongly bound to SHBG (sexual connection of steroid globulin) and makes up 54-70%.
- It binds to protein albumin by an unstable bond-about 25-43%.
- Free testosterone, which is the most biologically available and active form – from 1 to 4%.
The second and third forms are biologically active. Only they can enter the cells and connect directly to specific receptors or turn into active 5A-dihydrotestosterone. Strong binding to SHBG does not allow testosterone to enter the cells, and therefore is not able to manifest its biological activity.
Total testosterone is the sum of all fractions of the hormone, including free testosterone.
In most laboratory diagnostic centers, only total testosterone is determined, which normally in men is 12-33 nmol / l. In some cases, this is quite enough. However, only such a study is not very informative and limits the doctor’s ability to carry out timely and differential diagnosis in cases, for example, in patients with obesity, metabolic syndrome, Type 2 diabetes mellitus.
In this regard, an additional definition is optimal:
- biologically active fractions, the average of which is 3.5-12 nmol / l ·
- free testosterone-4,25-42 pg / ml.
Age and testosterone regulations
All listed indicators of the hormone norm are moderate. They do not take into account fluctuations in different age periods. The concentration of total testosterone in men begins to decrease from 50-55 years by 0.8-1.6% per year, and by the age of 80 an average of 60%, compared to men of 20 years. The content of biologically active hormone in the blood is maximum at the age of 25-35 years, after which it annually decreases by 2-3%.
Indications for controlling the level of free testosterone:
Determination of the level of free testosterone in the blood serum in men is recommended when:
- violations of sexual development and testosterone synthesis, as well as early puberty in boys.
- Reifenstein Syndrome;
- pathology of the hypothalamic-pituitary system;
- cryptorchidism and myotonic dystrophy.
- dysfunction of the adrenal cortex.
- suspicion of an adrenal or testicular tumor;
- pathology of the gonads after testicular injury, viral mumps.
- chronic alcoholism
- reception of antiandrogenic drugs and gonadoliberins;
- old times.