A blood test can measure the amount of glucose in your blood. You fast overnight or for eight-hours during the day, and then take a blood test to measure your glucose levels. If your blood sugar is 126 mg/dl or above, you have diabetes. If you are overweight and don't exercise three times a week, you may be at risk. Some doctors recommend everyone over the age of 45 be screened for diabetes as you are more likely to develop the condition as you get older. Finally, if someone in your family has diabetes, you have a higher risk of having it as well.