4 year old with elevated blood sugar level?

My 4 year old son had blood work done the other day and the results showed that he had a elevated blood sugar level. His ped wants to do a fasting blood check and then two hours after eating. His blood sugar was 159 from the other day and also had ketones in his urine but no sugar. He didn't eat anything before the blood test just a cup of oj about two hours prior. What could be going on with my son?