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 those in the brain. Carbohydrates (or carbs) 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 called insulin and glucagon help control blood glucose levels.
Random blood sugar; Blood sugar level; Fasting blood sugar
How the test is performed
A blood sample is needed. For information on how this is done, see: Venipuncture.
How to prepare for the test
The test may be done in 2 ways:
After you have not eaten anything for at least 8 hours (fasting)
At any time of the day (random)
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
Your doctor may order this test if you have signs of diabetes. However, other tests (glucose tolerance test and fasting blood glucose test) are better for diagnosing diabetes.
The blood glucose test is also used to monitor patients who have the diabetes. It may also be done if you have:
A change in behavior
Seizures for the first time
If you had a fasting blood glucose test, a level between 70 and100 milligrams per deciliter (mg/dL) is considered normal.
If you had a random blood glucose test, normal results depend on when you last ate. Most of the time, blood glucose levels will be below 125 mg/dL.
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What abnormal results mean
If you had a fasting blood glucose test:
A level of 100-125mg/dL means you have impaired fasting glucose, a type of prediabetes. This increases your risk for type 2 diabetes.
A level of 126 mg/dL and higher most often means you have diabetes.
Higher-than-normal random blood glucose levels may be a sign of diabetes. In someone with diabetes, it may mean the diabetes is not well controlled. Your healthcare provider will likely order a fasting blood glucose or a glucose tolerance test, depending on your random test result.
Other medical problems may also cause higher-than-normal blood glucose levels, including:
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.