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Sex hormone-binding globulin

 
, medical expert
Last reviewed: 08.07.2025
 
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Sex hormone binding globulin is a serum glycoprotein that, by binding to sex steroids (testosterone, estradiol, progesterone, etc.), regulates their biological activity.

Globulin is mainly formed in the liver, estrogens stimulate and testosterone suppresses its synthesis formula for calculating the free androgen index ISA*kOT/kGSPG*100 where:

  • ISA - free androgen index
  • TTC - total testosterone concentration
  • cSHBG - sex hormone binding globulin concentration

The free androgen index in young men ranges from 70 to 100%. When the free androgen index falls to 50%, signs of androgen deficiency usually appear. If the SHBG concentration decreases, the ratio of free testosterone to free estradiol increases, although there is an absolute increase in the concentration of both hormones. If the SHBG concentration increases, the ratio of free testosterone to free estradiol decreases. That is, the result of an increase in the SHBG concentration is an increase in the effects of estrogens. With age, there is an increase in the secretion of sex hormone-binding globulin, which can lead to both an increase in the effects of estrogen in men (gynecomastia, redistribution of adipose tissue according to the female type), and maintenance of the level of total testosterone within normal values with a decrease in the level of free testosterone.

Factors Affecting the Blood Concentration of Sex Hormone Binding Globulin
Factors that increase SHBG concentration Factors that reduce SHBG concentration
Estrogens Androgens
Hyperthyroidism Glucocorticoids
Cirrhosis Insulin
Hepatitis Hypothyroidism
Age Malnutrition
Situations associated with protein loss
Obesity
Prolactin
Growth hormone
Nephrotic syndrome
Malabsorption

In theory, all non-aromatizing AAS lead to a decrease in the concentration of SHBG in the blood plasma. In practice, the most pronounced decrease in SHBG occurs in the case of oral stanozolol. With aromatizing AAS, things are more complicated: they can both decrease and - by converting into estradiol or simply by exhibiting estrogenic activity - increase the level of sex hormone binding globulin.

A very sharp decrease in the concentration of SHBG in the blood plasma can lead to the same negative result as a sharp increase. If in the second case there is a decrease in the level of free testosterone and a change in the testosterone/estradiol ratio in favor of the latter, then in the first case testosterone can be destroyed before it is delivered to muscle cells - sex hormone binding globulin still performs a transport function.

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