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Free Hormone Fractions

Meaning

Free Hormone Fractions represent the small, unbound percentage of steroid and thyroid hormones circulating in the plasma that are biologically active and capable of diffusing across cell membranes to interact with intracellular receptors. The vast majority of hormones are bound to carrier proteins, such as Sex Hormone-Binding Globulin (SHBG) or albumin, which render them temporarily inert and act as a reservoir. Measuring these free fractions provides the most accurate assessment of an individual’s true hormonal status and tissue exposure. They are the only portion of the hormone pool that can exert immediate physiological effect.