Cushing’s syndrome — endogenous hypercortisolism — is characterized by a loss of normal 24 hour rhythm in cortisol secretion (circadian rhythmicity). In healthy patients, cortisol levels peak in the early morning hours and decrease to substantially lower levels at night. Rather than the normal decrease in late evening cortisol, patients with Cushing’s syndrome of any cause fail to fully decrease cortisol secretion in the late evening. Therefore, the measurement of an increased late evening cortisol is helpful in making the diagnosis of Cushing’s syndrome. Obtaining a late night, unstressed blood (serum) cortisol sample is virtually impossible in most clinical practices. Salivary cortisol is in equilibrium with and reflects the free, biologically active portion of cortisol in the serum. Therefore, if one obtains several saliva samples in patients at bedtime in their homes under unstressed conditions, one can make or exclude the diagnosis of endogenous hypercortisolism.
Our lab (ACL) and many other reference labs use a simple way to sample saliva using a Salivette made by the Sarstedt Company (Newton, NC). This device consists of a cotton tube and plastic tubes. The patient only has to place the cotton tube in the mouth, let it soak up saliva for 2-3 minutes and place it in the plastic tube. The tube is then mailed to our lab for analysis. There are other ways to obtain a saliva sample such as spitting in a tube or allowing passive drool into a tube; all of these approaches work for the measurement of cortisol in saliva. The analytical method used at ACL Labs is FDA cleared for the diagnosis of Cushing’s syndrome*. Salivary cortisol analysis is also available from most reference laboratories so it is available to clinicians around the world.
It is currently recommended to obtain 2 salivary cortisol samples on different evenings (often but not necessarily consecutive) at home between 11 PM and midnight in any patient in whom Cushing’s syndrome is suspected (see comments on sampling below). If these results are abnormal, the diagnosis can be confirmed using the low dose dexamethasone suppression test or urine free cortisol (or additional late-night salivary cortisol measurements). Due to the convenience of sample collection, the patient can sample saliva several evenings in a row. In fact, our clinical endocrinologists routinely order 2-3 consecutive late-night salivary cortisol samples. The results of many studies have shown that the measurement of several late-evening salivary cortisol is very accurate in diagnosing Cushing’s syndrome in most patients (Carroll T, Raff H, Findling JW. Late-night salivary cortisol for the diagnosis of Cushing’s syndrome: a meta-analysis. Endocrine Practice 15:335-342, 2009; Raff H. Cushing’s syndrome: diagnosis and surveillance using salivary cortisol. Pituitary 15:64-70, 2012).
It has now been demonstrated that late-night salivary cortisol measurements are also very useful in following patients with Cushing’s disease after pituitary surgery and perhaps even during medical therapy (Raff H, Carroll T. Cushing’s syndrome: from physiological principles to diagnosis and clinical care. J. Physiol. (UK) 593:493–506, 2015). It is recommended that if a patient feels symptoms returning or, perhaps, once a year, late-night salivary cortisol assessment should be performed.
Comments on Saliva Sampling
As stated above, ACL currently uses the Salivette to sample saliva. This involves placing a cotton swab in the mouth for 2-3 minutes so it is completely soaked with saliva. It is fine to chew the cotton swab, although one should not suck on it. The objective is to get the cotton swab as wet with saliva as possible. The cotton swab is then returned to appropriate compartment in the Salivette, tightly capped, and returned to the laboratory.
There are some important factors of which the patient should be aware. If possible, try not to handle the cotton swab. One simple way to avoid this is to place your hands in a plastic bag (like a sandwich bag). The reason this is important is to avoid contaminating the cotton swab with anything on the hands. Of particularly concern are ointments and creams many of which contain cortisol (hydrocortisone) – contamination of the lips, hands, and cotton swab with cortisol will render the saliva obtained useless. It is advisable to avoid teeth brushing and drinking water for a few hours before sampling. Alcohol intake should be avoided on the day of sampling as should smoking. It would also be prudent to avoid sampling on a day that has been particularly stressful. Patients on renal dialysis should sample saliva in the evening of a non-dialysis day.
*Doctors can obtain a kit by contacting ACL Client Services at 1-800-624-3134 or 1-800-877-7016.
By Dr. Hershel Raff, PhD, Winter, 2016
Editor’s Note: This article originally appeared in the Fall, 1998 issue of the Cushing’s Support and Research Foundation (CSRF) newsletter and was updated in August, 2016. Dr. Hershel Raff, PhD is a Professor of Medicine and Physiology at the Medical College of Wisconsin’s Endocrine Research Laboratory at Aurora St. Luke’s Medical Center in Milwaukee, Wisconsin.