Direct assay of cortisol in human saliva by solid phase radioimmunoassay and its clinical applications.

Direct determination of cortisol (F) in human saliva and its clinical applications were investigated. For this purpose, a solid phase radioimmunoassay (RIA) was carried out. The detection limits for F in 50 and 400 microliter of saliva were 0.125 and 0.0156 micrograms/100 ml, respectively, and the intra-assay coefficient of variation was 5.9--12.2%. Salivary F levels measured by this method were in good agreement with those by the RIA after extraction with dichlormethane reported previously. Salivary F levels were studied in 10 healthy adults with regard to diurnal rhythms, in rapid ACTH tests, and following intravenous injections of 20 mg F, and they showed almost similar changes to serum unbound F levels. Diurnal variations of salivary F in 8 normal children were nearly the same as those in healthy adults. In patients with Cushing's syndrome, neither normal diurnal rhythm of salivary F nor suppressed salivary F with dexamethasone were observed. Patients with adrenocortical insufficiency showed a lack of responsiveness in salivary F levels to stimulation with ACTH or lysin-vasopressin. These findings suggest that salivary F can be measured directly by the solid phase RIA and accurately reflects serum unbound F. The method is simple, accurate and useful for assessing adrenocortical function, especially in pediatric subjects and/or outpatients.