Salivary cortisol assessment in the evaluation of hypothalamic-pituitary-adrenal function

A simple, short and sensitive direct radio-immunoassay technique for the determination of salivary cortisol concentration was employed to assess saliva as a medium for evaluating cortisol response during endocrine testing in 9 controls and 40 patients. Results in controls suggested that an adequate salivary cortisol response to insulin hypoglycaemia was an increase of 150% above the basal value with a minimum peak of 15 nmol/l. Thirty-three patients were classified as being either good or poor responders to insulin hypoglycemia on the basis of criteria for plasma cortisol levels. When the defined salivary cortisol response was used for assessment, all 33 patients were correctly categorized into the same response groups. The salivary cortisol response to intramuscular tetracosactrin in 3 patients and an intravenous dexamethasone infusion in 4 patients confirmed the value of saliva as an assay medium. These studies show that the salivary cortisol response parallels that of total plasma cortisol in all cases. However, with sampling at short intervals a lag in secretion of the free fraction from the plasma into the saliva becomes apparent. The relative change in cortisol levels from the basal value is greater in saliva than in plasma.