Fasting blood glucose 9.1mmol/L may be diabetes mellitus, the diagnosis of diabetes mellitus needs to be determined by a professional doctor based on clinical symptoms and test results. The diagnosis of diabetes mellitus is based on the typical symptoms of “three more and one less” (drinking more, urinating more, eating more, and losing weight) plus the measurement of venous plasma glucose ≥11.1mmol/L at any time of the day, fasting blood glucose ≥7.0mmol/L, or 2-hour glucose ≥11.1mmol/L after glucose tolerance test, which can be diagnosed as diabetes mellitus if one of them meets the diagnosis. One of them is enough for a diagnosis of diabetes mellitus. When fasting blood glucose 9.1mmol/L is found, it is recommended to go to a regular hospital endocrine consultation in time to avoid delaying the condition.