Making the Diagnosis
Diabetes is diagnosed with simple blood tests. Your doctor may diagnose diabetes if the level of glucose in your blood after 8 hours of fasting is above 126 mg/dL (7.0 mmol/L). If your fasting blood glucose is 110 mg/dL to125 mg/dL (6.1 mmol/L to 6.9 mmol/L), then you may have a condition known as impaired fasting glucose (IFG), and may later develop diabetes. Diabetes is also diagnosed if a blood glucose level taken 2 hours after eating is greater than 200 mg/dL (11.1 mmol/L). It is important to note that one high blood glucose reading does not mean you have diabetes. In most cases, at least 2 high blood glucose readings are required before your doctor will make a diagnosis. Your doctor may also examine your eyes for signs of damage to the blood vessels of the retina (back of the eye).
Doctors may also diagnose diabetes based on the results of an oral glucose tolerance test (OGTT). With this test, a person fasts and then is given some glucose, after which their blood glucose is tested at various times to determine how quickly the sugar travels out of the bloodstream and into cells.