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Dexamethasone Suppression Test, High-Dose
|Test group||Dexamethasone Suppression Test|
|Sample type||see Cortisol|
|Normal range||See Additional Information|
|Additional information||For Differential Diagnosis of Cushing's Syndrome.
Rapid Test (based on Tyrrell JB et al. Ann Intern Med 1986;104:180.: Obtain a baseline serum cortisol at 0700-0800 hours. Administer 8.0 mg po dexamethasone that evening at 2300 hours and obtain another serum cortisol at 0700-0800 hours the following morning. Interpretation: A positive response (suppressibility) is a reduction of the post-dexamethasone serum cortisol to <=50% of the baseline cortisol level (sensitivity 89%, CI 80-94%; specificity 100%, CI 84-100%).
Standard Test (based on Liddle GW. J Clin Endocrinol Metab 1960;20:1539): Obtain a baseline serum cortisol at 0700-0800 hours and a 24 hour urine collection of urine for 17-OH corticosteroids beginning at the same time. On the following day administer 2.0 mg po dexamethasone q6h for 8 doses. Repeat the 24 hour urine 17-OHS collection during day 2 of dexamethasone administration and repeat the plasma cortisol at 0700-0800 hours on the morning after the last steroid dose. Interpretation: A positive response (suppressibility) is a reduction in both assays to <=50% of baseline values (sensitivity 92%, CI 82-97%; specificity 94%, CI 85-97%).
Significance: A positive response generally indicates an ACTH-producing pituitary tumor, rather than an ectopic (primarily thoracic) ACTH-producing tumoror an adrenal source.
|Last Updated||10/15/2008 9:50:01 AM|