What is a fasting blood glucose test for 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.

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.

Continue Learning about Diabetes


Diabetes mellitus (MEL-ih-tus), often referred to as diabetes, is characterized by high blood glucose (sugar) levels that result from the body’s inability to produce enough insulin and/or effectively utilize the insulin. Diabetes ...

is a serious, life-long condition and the sixth leading cause of death in the United States. Diabetes is a disorder of metabolism (the body's way of digesting food and converting it into energy). There are three forms of diabetes. Type 1 diabetes is an autoimmune disease that accounts for five- to 10-percent of all diagnosed cases of diabetes. Type 2 diabetes may account for 90- to 95-percent of all diagnosed cases. The third type of diabetes occurs in pregnancy and is referred to as gestational diabetes. Left untreated, gestational diabetes can cause health issues for pregnant women and their babies. People with diabetes can take preventive steps to control this disease and decrease the risk of further complications.

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