Fasting blood glucose generally should not exceed 12 hours, mainly because the test results at this time may be low, and too long a period of fasting is prone to cause hypoglycemia, dizziness, coma and other adverse reactions. The general testing time for fasting blood glucose is 8 to 10 hours of fasting, usually not more than 12 hours, after which the early morning fasting blood glucose value is measured. Blood glucose testing within the specified time can accurately observe the changes in blood glucose, which is of reference value. Fasting blood glucose test time if more than 12 hours, the test results may be low, and patients are prone to hypoglycemic reaction. Blood glucose testing should be conducted under the guidance of a physician to comprehensively assess the blood glucose value for targeted management.