A fasting blood sugar over 126 mg/dl or two random blood sugars over 200 mg/dl would mean a diagnosis of diabetes.
I would do a fasting blood sugar on her tomorrow morning. Does she exhibit any of the common symptoms of diabetes like extreme thirst and hunger, frequent urination, weight loss?
A random blood sugar of 150 itself is probably not enough to diagnose diabetes.
I wish you the best of luck.
I would not be too concerned with a 150 after eating two hours prior. You might want to check your child's BS in the morning though just to be sure that it has come back down to normal. I'm not a doctor but I am a type I diabetic myself and have two children. They are teens now but I had them checked for diabetes a couple of times over the course of the last 5 years. There is a blood test they took that checked to see if they had markers to show if they would develop diabetes within the next couple of years. Fortunately, both kids were negative. You might want to consider getting that test for your child if it would put your mind at ease. If your doctor is unfamiliar with the test, check with the Jouvenile Diabetes Association and they could probably direct you. We live near Dallas, TX and had our tests done at a local hospital. At the time, they had many sites giving the test in our area, however, the last one my kids had was a couple of years ago.
Of course it could be a fluke and a meter error, but, I think you are right to be concerned with a 150 mg/dl post prandial bg in a child, especially if it's repeatable. Does your child exhibit any other symptoms of type 1 - excessive thirst, excessive urination, unexplained weight loss, lethargy....? I would check again 2 hours after eating a meal that has carbs. If it's high again, I would discuss it with a pediatric endocrinologist. An A1C test may be in order , at least as a baseline. Toddlers can decompensate very quickly if they have diabetes, so keep careful watch and avoid DKA at all costs.
I personally feel that a post prandial blood glucose reading is much more telling than a fasting bg; it lets you know if the islets are producing enough insulin to match the glucose circulating in the blood.
If there are no other symptoms and that was a one time high bg reading on a meter, I would not necessarily rush to have antibody testing done. As a parent of a child who had the antibody testing done on a sibling of my child with diabetes, the "positive" result was very disturbing; especially since there is NOTHING anyone can do to prevent onset or predict IF or WHEN onset MAY occur. Think about how that black cloud can hang over a child's head if the antibody testing turns out to be positive.
There is a wonderful website where you can get support: www.childrenwithdiabetes.com/chat in the parents room...if you want to chat with other parents of children with diabetes.