@654321 - The HPA is the hypothalamic-pituitary-adrenal axis. I have not had this test. Any of this type of test you would need would be ordered by an endocrinologist. My husband does medical research and he is the reason that I had the ACTH Stimulation Test. The doctors never suggested the test. They draw blood first which is a baseline and then give you an injection to stimulate the adrenal gland (adrenocorticotropic). They draw blood again at 30 minutes and then at 1 hour. I was at 12 when they drew the blood and then 16 at 30 min and 18 at an hour. The Endocrinologist said the results were great. Now just hoping all goes well with the tapering. These test normally have to be ordered and interpreted by an Endocrinologist. Mayo sent me to the in-house Endocrinologist and she said she would do any tests requested by Neurology.