Blood sugar may be high or low after fasting for a long time. Normally, after a long period of fasting, the blood glucose value in the body will drop. However, when the blood glucose value is low to a certain extent and the body has not eaten, the body will secrete such as catecholamines, glucocorticoids, growth hormone, thyroid hormone and other hormones that raise blood sugar, prompting blood glucose to maintain to a relatively normal level, when measuring blood glucose will be in the range of normal values or higher. It is worth noting that some diabetic patients fasting time is too long, the blood glucose may be lower than the actual blood glucose indicators, it will be easy to misdiagnosed as better blood glucose control. Some diabetic patients are extremely sensitive to their own glucose regulation, and after a long fasting time, their blood glucose will be higher than the actual blood glucose level. It is recommended that people test their blood glucose regularly to monitor for diabetes and hypoglycemia. If there is a history of diabetes in the family, it is important to pay attention to abnormal blood glucose values and seek medical attention in a timely manner.