Blood sugar refers to the concentration of glucose in the blood, and the value of blood sugar 4 hours after a meal, basically fasting blood sugar. However, due to the different populations, the specific range is different and cannot be generalized.1. General population: generally 3.9-6.1mmol/L. If it is during the day, 4 hours after meal usually has reached the next meal before the meal, and thus can refer to the fasting blood glucose value. If a patient has abnormal blood sugar, a glucose tolerance test can be performed to detect the specific blood sugar value. For the glucose tolerance test, fasting blood glucose values are measured on an empty stomach, followed by drinking 200 ml of liquid dissolved with 75 g of glucose. After drinking the glucose water, the blood glucose level is tested at 30 minutes, 1 hour, 2 hours and 3 hours, and then compared to the normal value. If abnormalities appear, consider the existence of abnormal glucose tolerance or the possibility of diabetes, at this time, you need to control according to the diabetic diet; 2. Diabetic patients: After suffering from diabetes, the blood sugar value 4 hours after meals is normal as long as it is maintained within 7.5 mmol/L. For diabetic patients, because the body’s glucose boosting hormone and glucose lowering hormone cannot be as sensitive as normal people, if the fasting blood sugar is controlled within strictly 3.9-6.1mmol/L, patients are prone to hypoglycemic symptoms. Therefore, patients should pay great attention to the fact that when blood sugar rises, they should strictly deal with managing their blood sugar according to the diagnosis of diabetes; 3. Gestational diabetes patients: fasting blood sugar of gestational diabetes patients needs to be paid attention to, in general, the normal value of fasting blood sugar of pregnant women is 3.1-5.6mmol/L. Pregnant women should control their own blood sugar, and it is recommended to eat less and more meals and eat breakfast regularly.