Salivary cortisol assays for assessing pituitary-adrenal reserve.

Cortisol concentrations were determined in matched samples of plasma and saliva from patients and healthy volunteers throughout the course of standard tests of pituitary and adrenal reserve. During insulin tolerance tests the percentage incremental changes in cortisol concentrations in saliva were strictly comparable with those in plasma and showed less inter-subject variance. The clinical decision taken with regard to the integrity of the pituitary-adrenal axis was the same whether plasma or salivary cortisol was measured. In the short tetracosactrin test changes in salivary cortisol reflected those in plasma and patients with loss of adrenal responsiveness would have been diagnosed as such using either measurement. In normal subjects, the circadian rhythm in salivary cortisol concentrations exactly paralleled that in plasma. Absence of the circadian rhythm in cases of hypercortisolism was seen as well in saliva as in plasma. Assays for salivary cortisol therefore provide information which is as clinically useful as that of plasma determinations. Since salivary cortisol concentrations were shown to reflect the free, biologically active fraction in plasma, salivary assay may, in selected cases, provide results of greater diagnostic significance than plasma total concentrations.