Blood sugar 7.9mmol/L depends on whether it is fasting blood sugar, or two hours after meal blood sugar. If it is a two-hour postprandial blood glucose, it is in the roughly normal range, not serious, only slightly higher than the normal value, and usually improves with a controlled diet. If it is fasting blood glucose 7.9mmol/L, it indicates the possibility of diabetes, and an OGTT test or another fasting blood glucose test can be performed. If it still reaches 7.9mmol/L, it can be diagnosed as type 2 diabetes. However, it is not very serious and needs to be strengthened with diet control and physical exercise. It is just found that diet control can be carried out at the beginning and no glucose-lowering drugs are needed.