One of the first things my endocrinologist checked was my insulin level. He suspected my insulin level would be high even though I had never been diagnosed with diabetes or prediabetes.
https://physicians.dukehealth.org/articles/even-low-doses-prednisone-creates-insulin-resistance
My endocrinologist was correct because my insulin level was high but my HbA1c and glucose levels were always borderline normal while I was taking prednisone. Nobody had ever checked my insulin level before.

My endocrinologist started me on Metformin because it is suppose to help prevent insulin resistance. He added that I should have been on Metformin during the entire time that I was taking prednisone for PMR. He said a high insulin level was a precursor to diabetes.
https://www.cdc.gov/diabetes/basics/insulin-resistance.html
My endocrinologist said that Metformin will only help with insulin resistance. My endocrinologist thinks that staying off prednisone along with diet and exercise will help more. Now I have to explain to other doctors why I take Metformin when I haven't been diagnosed with diabetes. I think Metformin is helping because now my HbA1C and glucose levels are well within the normal range and aren't borderline anymore. I will ask my endocrinologist to recheck my insulin level when I see him again.