What Causes Elevation In Blood Sugar Levels Post Steroid Infusion?

I had a steroid IV infusion today - finished about 2:30. I came home and made some spaghetti for dinner. I took 1 Metforin . I took my blood sugar at 8 pm and had a reading of 244 - I took it again and score 269. I took one more metformin and drunk some orange juice and some tomato juice. I may need insulin as I am suppose to go back Thursday and Friday to complete sterid infusion. I was pre diabetic before steroid infusion. Do not want diabetis.