A 15-hour fasting blood glucose may not be accurate. Measuring fasting blood glucose generally requires 8 to 10 hours of fasting. Measuring fasting blood glucose generally requires 8 to 10 hours of fasting, usually measuring blood glucose overnight in the early morning. Fasting for 15 hours for blood collection and testing of blood glucose values may be inaccurate, especially in patients with diabetes, too long a period of starvation may be hypoglycemic, in which case the fasting blood glucose value is inaccurate. Once the symptoms of hypoglycemia appear, sugar water or sugary food should be given in time. If the symptoms do not get better or worsen significantly, it is recommended to consult a doctor for intravenous glucose infusion in time. Fasting blood glucose is an important test to help diagnose diabetes, and should be performed in strict accordance with medical advice. If there are special circumstances can be timely communication with the doctor.