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What is a fasting blood glucose test for diabetes?

A fasting blood glucose (FBG) test is a check of a person's blood glucose level after the person has not eaten for 8 to 12 hours (usually overnight). This test is used to diagnose prediabetes and diabetes. It is also used to monitor people with diabetes.

Normal fasting blood glucose is below 100 mg/dl. A person with prediabetes has a fasting blood glucose level between 100 and 125 mg/dl. If the blood glucose level rises to 126 mg/dl or above, a person has diabetes.

Emilia Klapp
Nutrition & Dietetics Specialist

Also called a fasting plasma-glucose test, this is the most common test to diagnose diabetes and also can indicate insulin resistance. It is a blood test done early in the morning, after fasting for at least eight hours.

A result of more than 126 mg/dL (milligrams per deciliter) is a provisional diagnosis of diabetes. The diagnosis must be confirmed with a second test. A normal test result is less than 100 mg/dL. A result of more than 100 but less than 126 mg/dL indicates prediabetes.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.