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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.
Random blood sugar; Blood sugar level; Fasting blood sugar
A blood sample is needed. For information on how this is done, see: Venipuncture.
The test may be done while you are fasting or at random.
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.
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:
Up to 100 milligrams per deciliter (mg/dL) is considered normal for a fasting blood glucose test.
Persons with levels between 100 and 125 mg/dL have impaired fasting glucose, a type of prediabetes. These levels are considered risk factors for type 2 diabetes and its complications.
Diabetes is diagnosed in persons with fasting blood glucose levels that are 126 mg/dL or higher.
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.
Higher-than-normal blood glucose levels (hyperglycemia) may be a sign of diabetes. In someone with diabetes, it may mean the diabetes is not well controlled.
Increased levels may also be due to:
Lower-than-normal levels (hypoglycemia) may be due to:
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Drugs that can increase glucose measurements include the following:
Drugs that can decrease glucose measurements include the following:
American Diabetes Association. Standards of medical care in diabetes -- 2011. Diabetes Care. 2011;32:S11-S61.
Inzucchi SE, Sherwin RS. Type 2 diabetes mellitus. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 248.