Salivary cortisol levels in true and apparent hypercortisolism

Area of Science:

• Endocrinology
• Clinical Chemistry
• Diagnostic Medicine

Background:

• Total plasma cortisol can be misleading due to variations in cortisol-binding globulin (CBG) capacity, influenced by pregnancy, drugs, or congenital conditions.
• Salivary cortisol, reflecting free cortisol, is less affected by protein binding alterations and is valuable for investigating hypothalamic-pituitary-adrenal disorders.

Purpose of the Study:

• To compare plasma and salivary cortisol measurements as indices of adrenal function.
• To differentiate true hypercortisolism from spurious hypercortisolism caused by oral contraceptives or pregnancy.
• To assess circadian variations and dexamethasone suppression responses in plasma and salivary cortisol.

Main Methods:

• Studied circadian variation of plasma and salivary cortisol in six patients with hypercortisolism and normal volunteers.
• Administered a dexamethasone suppression test via continuous infusion (1 mg/h) to five patients with pituitary-dependent Cushing's disease, one with adrenal carcinoma, and seven normal subjects.
• Measured endogenous cortisol half-life in plasma and saliva during dexamethasone infusion.

Main Results:

• Normal subjects showed significantly higher plasma and salivary cortisol at 0900 h compared to 2400 h.
• Patients with Cushing's syndrome lacked a significant circadian difference in plasma and salivary cortisol.
• Adrenal carcinoma patient exhibited failure of suppression in both plasma and salivary cortisol during dexamethasone infusion; pituitary-dependent Cushing's disease patients and normal subjects showed no significant difference in cortisol half-life.

Conclusions:

• Salivary cortisol provides a more accurate reflection of free cortisol and adrenal function, particularly in conditions affecting CBG.
• Circadian rhythm assessment of salivary cortisol can aid in diagnosing hypercortisolism.
• Dexamethasone suppression testing using salivary cortisol is effective, especially in differentiating adrenal carcinoma from pituitary-dependent Cushing's disease.