Serum free cortisol freely diffuses into saliva. Therefore, measurements of salivary cortisol (hydrocortisone) more accurately reflect the serum free cortisol. The salivary cortisol concentration is independent of salivary flow rate.
Normal range: varies diurnally, with concentrations about 5.6 ng/mL at 8:00 " “9:00 am and about 1 ng/mL at 11:00 pm.
Use
Screening for Cushing syndrome.
Diagnosis of Cushing syndrome in patients presenting with symptoms or signs suggestive of the disease.
Assessing cortisol secretion serially in ambulatory patients. Measurements are helpful in patients with cyclical Cushing syndrome.
Interpretation
Late evening levels are increased in Cushing syndrome.
Morning levels are decreased in adrenal insufficiency.
Limitations
Several factors influence analytical measurement and accuracy of salivary cortisol levels, including collection processes, devices, sample handling, processing and storage, and choice of analytical method.
Changes in cortisol-binding globulin and albumin affect total cortisol levels but not free levels in serum and saliva.