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Blood Sugar and the Dexamethasone Suppression Test

Question: I am being tested for Cushing’s and my blood sugars are already running 400-600. I have been asked to do an overnight dexamethasone suppression test. I am afraid that the dex will further increase my blood sugar. Do you have any suggestions?

Answer: Dexamethasone can increase blood sugar. You definitely should not receive dexamethasone until your glucose control improves significantly, due to risk of a diabetic coma. There are indications that very poorly controlled diabetes can falsely elevate cortisol levels, so glycemic control should be “reasonable” before testing for Cushing’s is started. If the patient obviously has Cushing’s, testing and treatment decisions need to be made on a case by case basis. While there are other tests for Cushing’s that could be done, the first priority would be to stabilize your blood sugar. “Reasonable” control for starting testing would be blood sugars consistently under 300 and an A1c that is less than 9.0-9.5%. This is not good control, but should be adequate to start testing.

By Dr. James Findling MD (Spring, 2009)


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