Hello, Since your father s blood sugars both fasting and post prandial (PP) were normal before surgery, the mild elevation after surgery is due to the stress related to surgery. It ought to settle in a couple of weeks. Did your father have an A1c done? It would show how his blood sugar has been for the past 3 months to know whether he had high blood sugar before or it is only induced by the stress Mild elevation in blood sugar for short periods do not do any harm. But a severe drop in blood sugar can be distressing and dangerous especially in a senior citizen. Also metformin ( melmet) is to be avoided in people with decreased kidney function which your father may have due to his age. So if I were his treating doctor, I would not give him metformin at this stage and wait for a couple weeks, check the blood sugar again. So my advice would be to wait and watch. Hope I have addressed your concern and if you have any further queries, please do not hesitate to contact me. Wish your father good health and a fast recovery. Dr. Noble Zachariah M.D.