yo need to see doctor and get the medicines to reduce the blood glucose levels, it is not safe to have blood glucose levels as high as 400, it will defenitely harm your kidney and eyes as well as other organs like heart and perepheral nerves and blood vessels. you also need to keep a good check on your weight and do regular exercie every day in the morning for atleast one hour. also the food need to be taken should be sugar free and need to take small and frequent meals. try consuming juice of bitter ground every day in the morning it will help in controling sugar levels.