This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of Adrenal Gland, Subject name: Medicine
[{'content': 'Which is the best test for diagnosis of adrenal insufficiency? \nSelect and explain. \nA. CT abdomen, B. Steroid autoantibodies, C. Fludrocoisone challenge test, D. Cosyntropin test', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The diagnosis of Primary Adrenal Insufficiency is established by Cosyntropin test Coisol values of <18ug/dl sampled 30-60 minutes after ACTH stimulation will diagnose the disease. This is followed by plasma ACTH values to identify primary versus secondary Addison disease. Steroid auto-antibodies are marker for Autoimmune Adrenalitis. Fludrocoisone challenge test is done for Conn syndrome.', 'role': 'assistant'}]