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Bioavailable Hormone Fractions

Meaning

This refers to the specific portion of total circulating hormones, such as testosterone or estrogen, that are unbound by carrier proteins like Sex Hormone-Binding Globulin (SHBG) or Corticosteroid-Binding Globulin (CBG), and are therefore capable of interacting with cellular receptors to exert a physiological effect. Measuring only total hormone levels often obscures the actual functional endocrine status of a patient. Clinical assessment demands understanding these free or loosely bound fractions for accurate diagnosis of hypogonadism or hypercortisolemia. The unbound state is the only fraction relevant for receptor binding and signal transduction.