- Last Update On : 2016-04-03
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). A salivary sample can be collected at home by the patient and then delivered to the laboratory the next morning.
Cortisol in plasma enters saliva by diffusion and ultrafiltration of the nonprotein bound fraction of cortisol. Salivary cortisol levels are assumed to represent free cortisol concentrations in blood.
Salivary cortisol samples are collected in Salivette tubes. Patients should be instructed to not brush or floss their teeth immediately prior to collecting the saliva sample to avoid contamination of saliva with blood. They should also refrain from eating 60 minutes prior to specimen collection. They need to wash out their mouth thoroughly with water 10 minutes before specimen collection.
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 concentrations can be close to the functional sensitivity of some assays. These assays may be very imprecise. The preferred method for measuring salivary cortisol is liquid chromatography – tandem mass spectrometry. Typical 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|
Contamination of saliva with blood can produce very high cortisol levels. Contamination of saliva with topical hydrocortisone can also lead to unusually high salivary cortisol results.
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.
Nieman LK, et al. The diagnosis of Cushing’s syndrome: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2008:93:1526-40.
Inder WJ et al. Measurement of salivary cortisol in 2012-laboratory techniques and clinical indications. Clin Endocrinol (Oxf) 2012;77:645-51.
Wood P. Salivary steroid assays-research or routine? Ann Clin Biochem 2009;46:183-96.