A nurse is teaching a school-age child who has type 1 diabetes mellitus and his parents about illness management. Which of the following instructions should the nurse include?

The correct answer is A: Test the urine for ketones. This instruction is crucial for monitoring diabetic ketoacidosis, a serious complication of type 1 diabetes. Ketones in the urine indicate inadequate insulin levels. Choice B is incorrect because blood glucose levels over 350 mg/dL are already very high and should prompt immediate action, not just notification. Choice C is incorrect as nausea can be a sign of hypoglycemia, and withholding insulin would worsen the situation. Choice D is incorrect as limiting fluid intake can lead to dehydration, especially during mealtime when blood sugar levels can fluctuate.