A method for finding out how much glucose (sugar) is in the blood. The test can show if a person has diabetes. A blood sample is taken in a lab or doctor’s office. The test is usually done in the morning before the person has eaten. The normal, nondiabetic range for blood glucose is from 4 to 6 mmol/l before meals and less than 8 mmol/l after meals, depending on the type of blood being tested.