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Testosterone and estradiol circulate in the bloodstream, bound mostly to SHBG (sex hormone binding globulin) and to some degree other blood proteins. Only a small fraction of the sex hormones are unbound, or "free," and thus biologically active and able to enter a cell and activate its receptor.
SHBG decreases the active form of the hormone available to the tissues. Thus bioavailability of sex hormones is influenced by the level of SHBG. High levels of insulin and androgens decrease SHBG level. On the other hand, thyroid hormone and estrogen increase it.
Conditions with low SHBG include ovarian cysts, diabetes, and hypothyroidism. Conditions with high SHBG include pregnancy, hyperthyroidism, and anorexia. There has recently been research to link high SHBG levels with breast and testicular cancer as well.
Fasting is not required for this test. Take all medications as prescribed. Do not take supplements the day of the test.
Any type of contraceptives that contain hormones will invalidate hormone results.