Cortisol-binding globulin (CBG) is a serum alpha-2-globulin-binding protein with high affinity and limited capacity for cortisol. It binds most (±92%) of the serum cortisol; the remaining cortisol (±8%) circulates in a free form or bound to albumin.
Cortisol-binding globulin (CBG) is synthesized in the liver. Circulating levels increase in pregnancy or after administration of estrogen or oral contraceptives. Insulin may inhibit synthesis, a fact that might explain the low CBG levels observed in hyperinsulinemic states (eg, diabetes, obesity, PCO).
Cortisol-binding globulin (CBG) levels are also reduced in:
- nephrotic syndrome,
- severe chronic liver disease.
The Cortisol-binding globulin (CBG) assay is helpful in assessing unexpected values of blood cortisol. Other assays useful in diagnosis and therapy of cortisol abnormalities include plasma cortisol, ACTH, β-lipotropin, urinary cortisol (by HPLC), or free cortisol in plasma or serum.
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