Simultaneous measurement of cortisol in serum and saliva after different forms of cortisol administration

To prove the clinical usefulness of cortisol measurements in saliva for the exact assessment of a patient's corticoid status under therapeutic hormone substitution, we measured simultaneously total cortisol in serum and non-protein-bound cortisol in saliva after administration of different forms of hydrocortisone (cortisol) in eight cortisol-suppressed, healthy male volunteers. The intravenous and oral administration of 20 mg of cortisol exceeds the binding capacity of the corticosteroid-binding globulin (CBG), leading to an increase of the ratio between salivary and serum cortisol at the higher cortisol concentrations in blood. After rectal administration of 100 mg of cortisol acetate, the serum cortisol concentration does not exceed the binding capacity of CBG, so the ratio between salivary and serum cortisol remains nearly constant. However, this ratio was higher after rectal administration than after intravenous and oral administration, probably because of weaker binding of the acetate form of cortisol to CBG. Thus, the salivary measurement of the non-protein-bound (i.e., biologically active) cortisol offers a convenient way to monitor the effectiveness of various forms of systemic corticoid substitution.