Dexamethasone – What is this test and what is it for.?

Patient: I went to my ENDOCRINOLOGY apt today and he told me that there was something strange about my examination , then he ordered me for labs blood drawn eight viles of it .. then he sent me to ultrasound .. then he told me he was gonna do a test on me for a VERY RARE diasease that involves a tumor …My question is .. what is the disease ? and why did he give me dexamethasone .. he told me to take it at 11pm tonight and go straight to the lab in the am ..? what is this test what is this pill..?

Doctor: The test ordered by your endocrinologist is an overnight dexamethasone suppression test to see the changes in the level of cortisol (a hormone) in the blood. This test is done to check for a condition known as cushing`s disease which is caused by a tumor of the pituitary gland. I hope you will find the information useful, I wish you well.