How Is Prediabetes Diagnosed?

If you are 45 years old or older, your doctor may recommend that you be tested for pre-diabetes, especially if you are overweight. Being overweight means your body mass index (BMI) is over 25. BMI is a measure of your weight relative to your height. If you’re not sure, ask your doctor if you are overweight.

Diabetes and pre-diabetes can be detected with one of the following tests:

A fasting glucose test measures your blood glucose after you have gone overnight without eating. This test is most reliable when done in the morning. Fasting glucose levels of 100 to 125 mg/dL are above normal but not high enough to be called diabetes. This condition is called pre-diabetes or impaired fasting glucose, and it suggests that you have probably had insulin resistance for some time. IFG is considered a pre-diabetic state, meaning that you are more likely to develop diabetes but do not have it yet.

A glucose tolerance test measures your blood glucose after an overnight fast and 2 hours after you drink a sweet liquid provided by the doctor or laboratory. If your blood glucose falls between 140 and 199 mg/dL 2 hours after drinking the liquid, your glucose tolerance is above normal but not high enough for diabetes. This condition, also a form of pre-diabetes, is called impaired glucose tolerance and, like IFG, it points toward a history of insulin resistance and a risk for developing diabetes.

These tests give only indirect evidence of insulin resistance. The test that most accurately measures insulin resistance is too complicated and expensive to use as a screening tool in most doctors' offices. The test, called the euglycemic clamp, is a research tool that helps scientists learn more about sugar metabolism problems. Insulin resistance can also be assessed with measurement of fasting insulin. If conventional tests show that you have IFG or IGT, your doctor may suggest changes in diet and exercise to reduce your risk of developing diabetes.

If your blood glucose is higher than normal but lower than the diabetes range, have your blood glucose checked in 1 to 2 years.

Even if you are younger than 45, consider getting tested if you are overweight and

• are physically active less than three times a week
• have a parent, brother, or sister with diabetes
• have high blood pressure
• have abnormal levels of HDL cholesterol or triglycerides, two types of blood fats
• had gestational diabetes—diabetes during pregnancy—or gave birth to a baby weighing more than 9 pounds
• are African American, American Indian, Hispanic/Latino, Asian American, or Pacific Islander
• have polycystic ovary syndrome
• have dark, thick, velvety skin around your neck or in your armpits
• have blood vessel problems affecting your heart, brain, or legs

If the results are normal, you should be retested in 3 years. If you have pre-diabetes, you should be tested for type 2 diabetes every year or two.