High fasting insulin may be prediabetes, or diabetes. Prediabetes includes impaired fasting glucose and impaired glucose tolerance. Impaired fasting blood glucose: fasting blood glucose greater than 6.1 but less than 7.0 mmol/L, 2-hour post glycemic load blood glucose less than 7.8 mmol/L; impaired glucose tolerance: fasting blood glucose less than 7.0 mmol/L, 2-hour post glycemic load blood glucose greater than 7.8 but less than 11.1 mmol/L. Diagnostic criteria for diabetes mellitus: fasting blood glucose ≥7.0 mmol/L, or 2-hour post glycemic load blood glucose ≥11.1 mmol/L, or random blood glucose ≥11.1 mmol/L, accompanied by three more and one less symptom (drinking, eating, urinating, and weight loss), diabetes mellitus can be diagnosed. Stress and infection can cause a transient increase in blood glucose. The occurrence of high fasting blood glucose should be timely to the hospital, a clear diagnosis, under the guidance of the doctor to choose a treatment plan.