Can creatinine levels be transiently high over baseline during hyperglycemia (sugar ~ 500)? Asking because creatinine values are normal when fasting

Yes. Depending on method for creatinine testing, presence of ketosis, that may accompany hyperglycemia, the result may be falsely elevated. Make sure to control your glucose and A1c. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex.