Diabetes

Frequently Asked Questions

15. How do doctors diagnose diabetes and pre-diabetes?

Doctors use the following tests to diagnose diabetes.

• A fasting plasma glucose, or FPG test measures your blood glucose after you have gone at least 8 hours without eating. Doctors use this test to detect diabetes or pre-diabetes.
• An oral glucose tolerance test, or OGTT measures your blood glucose after you have gone at least 8 hours without eating and 2 hours after you drink a sweet beverage. Doctors also use the oral glucose tolerance test to diagnose gestational diabetes in pregnant women.
• An A1C test measures your average blood glucose levels over the past 3 months. It can be used to diagnose type 2 diabetes and pre-diabetes. It does not require fasting and blood can be drawn for the test any time of the day.
• In a random plasma glucose test, the doctor checks your blood glucose without regard to when you ate your last meal. This test, along with an assessment of symptoms, is used to diagnose diabetes but not pre-diabetes.

If any of these tests show that you might have diabetes, your doctor will need to repeat the test with a second measurement unless there are clear symptoms of diabetes.