Measurement of salivary cortisol, which evaluates the free form of the hormone, has become popular following the development of commercial assays. This article evaluates the different assays available for measurement of salivary cortisol, and its clinical application in some physiological and pathological conditions. Measurement of salivary cortisol has been extensively used to evaluate cortisol circadian rhythm and adrenal insufficiency, in the first days of life of full-term and pre-term infants, and to evaluate the hypothalamic-pituitary-adrenal axis (HPA) activity in adults and children with cognitive impairment, major depression, stress, anxiety, panic syndrome, chronic fatigue syndrome, and sleep deprivation in shift workers. Measurement of salivary cortisol is also used in the diagnosis of Cushing syndrome, in adults and children. These studies demonstrate that midnight salivary cortisol measurement has higher diagnostic sensitivity compared to all other previously analyzed parameters, in detecting Cushing syndrome (CS), even in patients with intermittent or mild hypercortisolism. Using salivary cortisol measurement, we evaluated the diagnostic accuracy of the high dose dexamethasone (DEX, 8mg and 24 mg) suppression test in the differential diagnosis of CS. Our data suggest that salivary cortisol compared to plasma cortisol improved the diagnostic accuracy of high dose DEX suppression tests, even using more rigorous criteria of suppression. It is critical that researchers and clinicians must be aware of the differences generated in different salivary cortisol assays, in order to interpret the intervals of references adequately. Thus, salivary cortisol assays should be chosen and interpreted based on assay-specific normative data in combination with results from patients suspected but proven not to have CS. We also suggest that commercial laboratories consider large-scale validation of these assays to make them widely available to practicing clinicians.
Salivary cortisol; Hypercortisolism; Dexamethasone suppression tests; Cushing's syndrome; Pseudo-Cushing
