Sex hormone-binding globulin

SHBG is a special protein (glycoprotein) that binds to sex hormones (androgens and estrogens) for their subsequent transportation in the body. It is formed in the liver.

Testosterone and estradiol are transported in the blood in a bound state - to a greater extent with SHBG, with albumin and with transcortin. This is necessary because free proteins are broken down very quickly in the blood by the action of various proteolytic enzymes. And only 1-2% of hormones are in the free state. Only these 1-2% of free hormones fulfill their biological function. As soon as the active fraction of the hormone comes into contact with the target organs, the carrier proteins "release" the hormone molecules, which again replenish the 1-2 active percentages.

Thus, SHGB is a kind of depot of sex hormones. However, if for some reason the concentration of SHGB increases, the amount of bound "inactive" hormone increases as well.

When the level of sex hormone (e.g. testosterone) is determined in the blood, the total amount of free and bound substance is implied. If we perform this study simultaneously with the determination of SHGB, we can get the index of free hormone, which is a more reliable criterion for diagnosing conditions of hormone disbalance. The calculation is made according to the formula:

 Testosterone Free Index (TFI) = total testosterone/SHGB*100%

SHGB has affinity with the following hormones (in descending order): DIHYDROTESTORONE->TESTOSTERONE->ANDROSTENEDIOL->ESTRODIOL->ESTRONE->DHEA (in insignificant amounts, DHEA-C is not bound). The amount of SHGB is directly related to androgens and estrogens: Androgens decrease SHGB production, estrogens stimulate it. For this reason, the level of SHGB in women is almost 2 times higher than in men.

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