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Midnight Salivary Cortisol Versus Urinary Free and Midnight Serum Cortisol as Screening Tests for Cushing's Syndrome

Gafni RI, Papanicolaou DA, Nieman LK.
Developmental Endocrinology Branch, National Institute of Child Health and Human Development, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892-1862, USA.

OBJECTIVE: There is currently no optimal test to screen for endogenous Cushing's syndrome (CS) in children. Traditional 24-hour urine or midnight serum cortisol values may be difficult to obtain or elevated by venipuncture stress. We hypothesized that salivary cortisol measurement is a reliable way to screen for CS in children.

STUDY DESIGN: Sixty-seven children (5-17 years) were studied: 24 obese volunteers, 29 non-obese volunteers, and 14 children with CS. Saliva was obtained at 7:30 AM, bedtime, and midnight for measurement of free cortisol by radioimmunoassay.

RESULTS: Salivary cortisol was detectable in all morning and evening samples from patients with CS but was frequently undetectable in healthy children at bedtime (66%) and at midnight (90%). With cut points that excluded healthy children, a midnight salivary cortisol value of 7.5 nmol/L (0.27 microg/dL) identified 13 of 14 patients with CS, whereas a bedtime value >27.6 nmol/L (1 microg/dL) detected CS in 5 of 6 patients. The diagnostic accuracies of midnight salivary cortisol and urinary free cortisol per square meter were the same (93%).

CONCLUSION: Salivary cortisol measurement at bedtime or midnight rules out CS in nearly all cases. Nighttime salivary cortisol sampling is thus a simple, accurate way to screen for hypercortisolism in children. PMID: 10891818 [PubMed - indexed for MEDLINE]

Salivary Cortisol: A Screening Technique

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.

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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