Ellen
I just saw your post and I had tpo reply.
I have been on pred for 7 years straight - I could never get off. Whenever I got to 3mg I would flare. Happened hundreds of times, and I was sick of it.
I read up on the net about adrenal glands, as I suspected they were the reason I kept getting sick. No Doctors would take me seriously. In the end, after a lot of complaining, I had a cortisol test done - which showed my cortisol level was dangerously low. But, I had to have another set of tests done to confirm the diagnosis. I had a synacthen test - and that confirmed I had Secondary Addisons Disease (secondary andrenal failure).
If only I had been given this test all those years ago I would not have had to endure all those flare-ups.
SO, long term pred has drastically reduced my adrenal function - and I now take a small dose of Hydrocortisone every day. Your taper of 7.5 and 0 would never have worked for me. It may work for you. I have been told it could take YEARS of me taking a tiny dose of steroid for my adrenals to start working again.
I have also been given an emergency steroid injection to keep at home.
Being on pred can affect the outcome of a cortisol test but there are ways around it. Your endocinologist can advise you.
I hope this helps.
Best of luck to you.