Fasting is defined as not eating carbohydrates, or beverages containing calories, etc. for at least 8 hours in the early morning, so fasting is required for fasting plasma glucose levels to be determined for at least 8 hours. Water does not contain carbohydrates or calories, so you can drink water when taking venous blood for plasma glucose level measurement on an empty stomach. Not only plasma glucose, but also liver function, thyroid function and other blood tests can be performed with water. The normal value of fasting blood glucose is 3.8-6.0 mmol/L. When fasting blood glucose is between 6.0-7.0 mmol/L, fasting blood glucose is considered to be too high and is considered pre-diabetic. When fasting blood sugar is greater than 7.0mmol/L, the diagnosis of diabetes may exist, so as long as the fasting blood sugar is greater than 6.0mmol/L, you need to give diabetic diet and exercise treatment, and regularly review the blood sugar.