Cushing's syndrome - endogenous hypercortisolism - is characterized by a loss of circadian rhythmicity. In normal 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 decrease cortisol secretion in the late evening. Therefore, the measurement of elevated late evening cortisol is helpful in the diagnosis of Cushing's syndrome. Obtaining a late night, unstressed plasma cortisol is virtually impossible in most clinical practices. Salivary cortisol is in equilibrium with the free, biologically active portion of cortisol in the plasma. Therefore, if one obtains a saliva sample in patients at bedtime in their homes under unstressed conditions, one can make the diagnosis of endogenous hypercortisolism.
A simple way to sample saliva is by 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 chew the cotton tube for 2-3 minutes and place it in the plastic tube. The tube is then transported to our lab for analysis.
Late-evening salivary cortisol is not intended to replace the current standard screening test - measurement of a 24 hr urine free cortisol. However, the salivary cortisol test can be extremely useful for patients suspected of having intermittent Cushing's syndrome. 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-evening salivary cortisol samples. Our research (Raff H, Raff JL, Findling JW. 1998 Late-Night Salivary Cortisol as a Screening Test for Cushing's Syndrome. J Clin Endocrinol Metab. 83:2681-2686) has shown that the combination of late-evening salivary cortisol and urine free cortisol is very accurate in diagnosing Cushing's syndrome in most patients. Doctors can obtain a kit by contacing ACL Client Services at 1-800-877-7016.
Editor's Note: Dr. Hershel Raff, Ph.D. is a Professor of Medicine and Physiology at the Medical College of Wisconsin's Endocrine Research Laboratory at St. Luke's Medical Center in Milwaukee, Wisconsin.
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