Dry mouth is not necessarily a manifestation of diabetes. Dry mouth is one of the symptoms of diabetes and can also be caused by inadequate fluid replacement due to low water intake and sweating. If symptoms such as persistent dry mouth, increased water intake and polyuria occur, patients are advised to have their blood glucose measured, such as fasting blood glucose >7.0mmol/L or 2 hours postprandial blood glucose >11.1mmol/L can be used as diagnostic criteria. Those who cannot confirm the diagnosis are recommended to have glucose tolerance test, which can be used as the diagnostic criteria of diabetes. If there are obvious symptoms of diabetes mellitus and weight loss, random testing of venous blood glucose >11.1mmol/L at any time can also be diagnosed as diabetes mellitus.