Sex Hormone Binding Globulin (SHBG) is a protein in the blood that binds sex hormones such as estradiol and testosterone. It is produced by the liver. Its key function is to transport sex hormones in the blood, and with that also regulating the amount of free sex hormones. If a sex hormone is bound to SHBG, it is considered inactive, and therefore has no function on the surrounding tissues. HBG is measured for example for the Free Androgen Index (FAI) to calculate the amount of free (and therefore active) testosterone in the body.
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