The causes of high blood glucose may include diabetes, improper diet, infection, stress, medication, etc. It is recommended to consult a medical professional for specific causes to avoid delay. Diabetes mellitus is a metabolic disease characterized by chronic hyperglycemia, which can lead to high blood glucose; eating a large amount of sweets or high-calorie foods may cause an increase in blood glucose levels; high blood glucose levels may also occur in the case of infection or stress; and if glucocorticoid medication is applied, it may also lead to an increase in blood glucose levels. Under normal circumstances, fasting blood glucose levels are between 3.9 and 6.1 mmol/L, and 2-hour postprandial blood glucose levels are below 7.8 mmol/L. Once elevated blood glucose levels are detected, prompt medical attention should be sought to clarify the cause of the condition.