Salivary Cortisol to Screen for Cushing's syndrome |
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Increasing numbers of obese, depressed, diabetic and hypertensive patients are presenting with clinical symptoms that mimic those of Cushing's syndrome including weight gain, poor wound healing, immune suppression and mood changes. However, Cushing's syndrome is extremely rare, occurring at a rate of only 5 cases per million individuals. With such a low incidence, establishing the diagnosis of Cushing's syndrome is a very challenging clinical and laboratory problem.
One of the earliest biochemical abnormalities in Cushing's syndrome is a failure to decrease cortisol secretion fully at its normal nadir late at night. However, obtaining a stress free blood sample at 11:00 pm or midnight for plasma cortisol determination is difficult in ambulatory patients. Recent studies in adults and children have convincingly demonstrated that an elevated late night or bedtime salivary cortisol sampling is an excellent screening test and has a sensitivity and specificity of greater than 90% (J Clin Endocrinol Metab 2006;91:3746-53).
False positive salivary cortisol results may be associated with hypertension, advanced age and psychiatric disorders. However, repeat testing is usually normal in these situations, but not in true endogenous Cushing's syndrome.
Salivary cortisol samples can be collected in Salivette tubes. Patients should be instructed to not brush their teeth prior to collecting the saliva sample. They should also refrain from eating or drinking 15 minutes prior to specimen collection and should avoid using hydrocortisone creams which may contaminate the specimen.
The specimen is collected by:
- Removing the cap to expose the swab
- Tipping the tube so that the swab falls directly into the mouth
- Rolling the swab in the oral cavity for one minute
- Spitting the swab back into the tube
- Capping the tube tightly
- Recording collection time on the tube
- Refrigerating specimen until delivered to a SLRL patient Service Center
Salivary cortisol is measured by liquid chromatography - tandem mass spectrometry. Time dependent reference ranges are listed below.
Time |
Salivary Cortisol (ng/dL) |
7 am - 9 am |
100 - 750 |
3 pm - 5 pm |
20 - 400 |
11 pm - midnight |
<100 |
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