A blood sugar 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. Glucose is a building block for carbohydrates. Carbohydrates are found in fruit, cereal, bread, pasta, and rice. Carbohydrates are quickly turned into glucose in your body. This can raise your blood glucose level.
Hormones made in the body help control blood glucose level.
A blood sample is needed.
The test may be done in the following ways:
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Your doctor may order this test if you have signs of diabetes. More than likely, the doctor will order a fasting blood sugar test.
The blood glucose test is also used to monitor people who already have diabetes.
The test may also be done if you have:
SCREENING FOR DIABETES
This test may also be used to screen a person for diabetes.
High blood sugar and diabetes may not cause symptoms in the early stages. A fasting blood sugar test is almost always done to screen for diabetes.
If you are over age 45, you should be tested every 3 years.
If you're overweight (body mass index, or BMI, of 25 or higher) and have any of the risk factors below, ask your health care provider about getting tested at an earlier age and more often:
Children age 10 and older who are overweight and have at least two 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 (3.9 and 5.6 mmol/L) 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 (6.9 mmol/L).
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.
If you had a fasting blood glucose test:
If you had a random blood glucose test:
Other medical problems can also cause a higher-than-normal blood glucose level, including:
A lower-than-normal blood glucose level (hypoglycemia) may be due to:
Some medicines can raise or lower your blood glucose level. Before having the test, tell your provider about all the medicines you are taking.
For some thin young women, a fasting blood sugar level below 70 mg/dL (3.9 mmol/L) may be normal.
There is little risk involved with having your blood taken.Veins and arteries vary in size from one person 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:
Reviewed By: 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, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.