High blood sugar does not necessarily mean diabetes. First of all, the diagnosis of diabetes mellitus refers to the typical symptoms of diabetes mellitus such as dry mouth, drinking, urinating, and weight loss, plus random blood glucose greater than or equal to 11.1mmol/L, or fasting blood glucose greater than or equal to 7.0mmol/L in glucose tolerance test, and 2-hour postprandial blood glucose greater than or equal to 11.1mmol/L in glucose tolerance test, and the diagnosis can be made when any two of the above three points are fulfilled. However, each point needs to be confirmed on another day, because human blood glucose fluctuates, and a high blood glucose at one time does not lead to a diagnosis of diabetes. There are many other reasons for false elevation of blood glucose, such as physiological reasons, such as overeating, mood changes, cold and hot stimuli, trauma, infection, and surgery and other stresses can cause an increase in blood glucose, but this elevation of blood glucose is usually transient, and when the stress is removed, the blood glucose will naturally return to normal. There are also some drugs, such as diuretics furosemide, hydrochlorothiazide, glucocorticoid prednisone, methylprednisolone, etc., and psychoneurotics such as olanzapine, but high blood glucose caused by drugs is as temporary as physiological causes, and blood glucose can be restored to normal after stopping the drugs. There are also liver function damage, pancreatic islet cell tumor, cortisolism and other special diseases can also cause a transient increase in blood glucose, blood glucose can be returned to normal after treatment of the disease. Therefore, it is necessary to clarify the degree of blood glucose elevation, clarify the cause of blood glucose elevation, discharge other causes of blood glucose elevation, and the value of blood glucose elevation reaches the diagnostic standard of diabetes before determining that it is diabetes mellitus.