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| |  ACP: Nighttime Salivary Cortisol Test Has Excellent Specificity and Sensitivity By Daniel Keller SAN DIEGO, CA -- April 7, 2003 -- Measurement of nighttime salivary cortisol levels provides excellent specificity and sensitivity to screen for Cushing's syndrome. In an update session on endocrinology at the Annual Session of the American College of Physicians here on April 4th, Glenn Braunstein, MD, said nighttime salivary cortisol testing is a practical and accurate way to distinguish between Cushing's and pseudo-Cushing's syndromes. The test is easy and convenient for the patient to do, said Dr. Braunstein, Chairman, Department of Medicine, Cedars-Sinai Medical Center, and Professor of Medicine, University of California Los Angeles School of Medicine. Pseudo-Cushing's may result from obesity, depression, anxiety, poorly controlled diabetes, alcoholism, liver disease, or excessive exercise. Dr. Braunstein told the audience that salivary cortisol measurements are superior to other screening tests for Cushing's syndrome -- they can be conducted at home in a non-sterile environment, and they eliminate the cost of an office visit and the potential for an increase in the cortisol level from the stress of venipuncture. In one study from the National Institutes of Health, saliva was collected by expectoration at 11:30 PM and midnight from 122 Cushing's patients, 21 pseudo-Cushing's patients, 23 patients with nonadrenal disorders, and 34 healthy controls. Radioimmunoassay was used to measure salivary cortisol. All subjects without Cushing's syndrome had low salivary cortisol levels, resulting in 100% specificity for detecting Cushing's syndrome. The sensitivity was 91% for the 11:30 PM collection time and 93% at midnight. The salivary cortisol test had better sensitivity and specificity for Cushing's syndrome than other detection methods, including a nighttime serum cortisol test and the dexamethasone suppression test. Only urine free cortisol tests had better specificity (94-98%). The concentration of cortisol in saliva is independent of salivary flow. Midnight salivary cortisol had a sensitivity of 84% in the differential diagnosis of pseudo-Cushing's, and only the midnight plasma cortisol test was more sensitive (89%). Dr. Braunstein said pseudo-Cushing's is a big problem in the differential diagnosis of Cushing's syndrome. The salivary cortisol test had "100% specificity for ruling out pseudo-Cushing's," he said. "So it is a very useful test to do right now in the Cushing's setting." He added that the test provides the opportunity for long-distance monitoring and follow up. The patient can collect a sample and mail it to a laboratory for measurement. Serial collection and assay of samples can pick up conditions of intermittent, periodic cortisol hyper-secretion. Nighttime salivary cortisol testing is also useful and has been validated for diagnosing Cushing's in children. Dr. Braunstein cautioned that a laboratory must be set up to run a calibrated, modified cortisol assay since the level of free (unbound) cortisol in saliva is only about 70% of the level in serum.
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