How does a doctor identify diabetes? Once symptoms appear, type 1 diabetes rarely goes undiagnosed for more than a few weeks. But even if you and your doctor suspect diabetes, testing is always necessary to confirm the diagnosis.

Fasting plasma glucose (FPG) test

This is the recommended diagnostic test for diabetes. "Fasting" means that no food can be eaten for 8 to 12 hours prior to the test — only water may be consumed. A blood sample is drawn from the arm or the back of the hand and analyzed for glucose level.

If there is any doubt that a patient truly has diabetes, two or more FPG tests may be done on different days to verify the results.

The doctor may do a plasma glucose test even if you have eaten in the past 8 hours. This is just a preliminary test, and results would likely need to be confirmed by a test after you or your child has fasted.

What does the FPG test reveal?

Normal fasting glucose levels are lower than 110 mg/dL. Patients whose glucose is between 110 mg/dL and 126 mg/dL have "impaired fasting glucose" and are at risk for developing type 2 diabetes, although they do not yet have diabetes.

When fasting glucose levels are 126 mg/dL or higher, the patient has diabetes. Usually people with type 1 diabetes have glucose levels that are "off the charts," often higher than 400 mg/dL. This is why it is very important to see a doctor right away if you suspect diabetes.