Use of saliva cortisol in the dexamethasone suppression test

In a sample of 26 inpatients (15 primary endogenous depressives and a heterogeneous comparison group of 11 psychiatric patients), results of the dexamethasone suppression test (DST) for endogenous depression were compared when cortisol was measured in plasma (total and free) and in saliva. Results showed a close linear relationship among plasma total and free cortisol, plasma total cortisol, and saliva cortisol, and between free plasma and saliva cortisol. A saliva cortisol cutoff point of 70 ng/dl achieved the same sensitivity (67%), specificity (91%), and diagnostic confidence (91%) as the best cutoff scores of plasma total cortisol (5 micrograms/dl) and plasma free cortisol (0.15 microgram/dl). These results suggest that saliva cortisol, which directly reflects the biologically active fraction of cortisol, can be used as a reliable and more practical index in the DST, especially in outpatients.