Joint Clinical Guidelines for Prednisone Induced Adrenal Insufficiency

Good stuff in my opinion!

This was how my endocrinologist approached my low cortisol level when I tapered off prednisone. I couldn't continue my taper with a low cortisol level. Only when my cortisol level improved was it safe to discontinue prednisone. Going from 3 mg to zero went quickly when my cortisol level was "adequate" and deemed to be safe by my endocrinologist.
https://academic.oup.com/jcem/article/109/7/1657/7667842?login=false
These are only guidelines ... as usual, you should consult your doctor and don't listen to internet tapering advice. People on the internet won't be able to order a morning cortisol level when you get to lower doses of prednisone.
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"R 2.7—If confirmation of recovery of the HPA axis is desired, we recommend morning serum cortisol as the first test. The value of morning serum cortisol should be considered as a continuum, with higher values more indicative of HPA axis recovery. (⊕○○○)

As a guide:

1. we suggest that the test indicates recovery of the HPA axis if cortisol is >300 nmol/L or 10 μg/dL and glucocorticoids can be stopped safely;

2. we suggest that if the result is between 150 nmol/L or 5 μg/dL and 300 nmol/L or 10 μg/dL, the physiologic glucocorticoid dose should be continued, and the morning cortisol repeated after an appropriate time period (usually weeks to months);

3. we suggest that if the result is < 150 nmol/L or 5 μg/dL, the physiologic glucocorticoid dose should be continued, and the morning cortisol repeated after a few months."