A blood glucose test measures the amount of a sugar called glucose in a sample of your blood.
Glucose is a major source of energy for most cells of the body, including brain cells. Carbohydrates are found in fruit, cereal, bread, pasta, and rice. They are quickly turned into glucose in your body. This raises your blood glucose level.
Hormones made in the body help control blood glucose level.
Random blood sugar; Blood sugar level; Fasting blood sugar; Glucose test
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
The test may be done in the following ways:
After you have not eaten anything for at least 8 hours (fasting)
Close relative with diabetes (such as a parent, brother or sister)
Children age 10 and older who are overweight and have at least 2 of the risk factors listed above should be tested for type 2 diabetes every 3 years, even if they have no symptoms.
If you had a fasting blood glucose test, a level between 70 and 100 mg/dL is considered normal.
If you had a random blood glucose test, a normal result depends on when you last ate. Most of the time, the blood glucose level will be below 125 mg/dL.
The examples above show the common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
If you had a fasting blood glucose test:
A level of 100 to 125 mg/dL means you have impaired fasting glucose, a type of prediabetes. This increases your risk of developing type 2 diabetes.
A level of 126 mg/dL and higher usually means you have diabetes.
If you had a random blood glucose test:
A level of 200 mg/dL or higher often means you have diabetes.
Pagana KD, Pagana TJ. Blood studies. Mosby's Manual of Diagnostic and Laboratory Tests. 5th ed. Philadelphia, PA: Elsevier Mosby; 2014:chap 2.
Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.