And It's About Time There Was Some Support For Cushing's!
From The Pituitary Center at Vanderbilt
Dexamethasone suppression tests are employed by The Pituitary Center at Vanderbilt in the evaluation of patients with Cushing's syndrome.
Dexamethasone suppression tests have been employed for more than 30 years in the evaluation of patients with Cushing's syndrome. Several variations have been developed since Dr. Grant Liddle of Vanderbilt first reported on the usefulness of the classical test in 1960.
The adrenal glands produce cortisol, the major glucocorticoid hormone in man, in response to signals provided by the pituitary gland. Dexamethasone is a synthetic glucocorticoid hormone. In normal subjects, daily doses of Dexamethasone in excess of 0.5-0.75 mg, can suppress the coordinated functions of the hypothalamus, pituitary and adrenal glands. Dexamethasone often fails to suppress the function of the hypothalamus, pituitary, and adrenal glands in patients with Cushing's disease or syndrome. These observations form the basis for the Dexamethasone suppression tests.
This test is a reasonable screening test for Cushing's syndrome. Dexamethasone 1.0 mg should be taken by mouth at 11:00 PM. A snack can be consumed with the medication. Report to the specified laboratory or physician's office so that a sample of blood can be obtained for determination of the serum cortisol level at 8:00 AM the very next morning.
This procedure is often employed in the diagnosis of Cushing's syndrome. Proper performance of the test requires precise timing and collection of urine samples as well as the ingestion of Dexamethasone at specified time intervals. Your physician may request that you collect several "basal" 24-hour urine samples for determination of free cortisol, 17-hydroxycorticosteroids, and creatinine.
The test begins on day one with the administration of the first of 8 doses of Dexamethasone. You may be asked to take the first dose at 6:00 AM. If so, subsequent doses should be at 12:00 noon, 6:00 PM, and 12:00 midnight on day one and then 6:00 AM, 12:00 noon, 6:00 PM, and 12:00 midnight on day two. You may be asked to begin the medication at some other time. If so, explicit guidelines will be provided to ensure that you understand when to take the subsequent doses of the medication.
Most importantly, the medication should be taken every 6 hours for a total of 8 doses.
You should begin the 24-hour urine collection at 6:00 AM on day two, coinciding with the 5th dose of the medication.
The urine collection should be completed at 6:00 AM on day three.
Please review the instructions for 24-hour urine collection.
Contact your physician if you have any questions.
This test is often employed in the diagnosis of Cushing's syndrome. It is rather unique in that it combines suppression and stimulation of the pituitary gland in order to gain additional information about the altered function of the hypothalamus, pituitary, and adrenal glands in patients with probable Cushing's syndrome.
A formal low dose Dexamethasone suppression test is performed as specified above, except that a 9th dose of Dexamethasone is taken at 6:00 AM on day three.
You should report to your physician's office by 8:00 AM for a CRH Stimulation Test on day three.
This test involves placement of an i.v. followed by injection of the hypothalamic hormone CRH, then sampling of blood for cortisol 15 minutes later.
This test is often employed in the differential diagnosis of Cushing's syndrome. It can help distinguish between Cushing's syndrome caused by pituitary tumors and non-pituitary tumors.
You should present to the specified laboratory or other location to have blood obtained for measurement of serum cortisol and ACTH at 8:00 AM on day one.
Take Dexamethasone, 8 mg, by mouth at 11:00 PM on day one. Present to the same facility at 8:00 AM on day two to have another sample of blood drawn for measurement of serum cortisol and ACTH.
This test is often employed in the differential diagnosis of Cushing's syndrome. It has largely been supplanted by the high dose 8 mg overnight Dexamethasone suppression test.
You should ensure that all collection bottles are labeled with your name, the start date of the collection, and as an extra precaution, indicate the day of the collection (day 1, day 2, and so on). Transport the specimens to the designated facility for testing.