Glucose test - blood

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Blood test

A blood glucose test measures the amount of sugar (glucose) in a sample of your blood.

See also:

• Glucose test - CSF
• Glucose test - urine
• Home blood glucose monitoring

Random blood sugar; Blood sugar level; Fasting blood sugar

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

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Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The test may be done while you are fasting or at random.

If you are having a fasting glucose blood test, you should NOT eat or drink for 6 hours before the test.

A random glucose test can be done at any time of the day, but results depend on what you drink or eat before the test, as well as your activity.

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. It is also used to monitor patients who have the disease.

The carbohydrates you eat eventually end up as glucose in the blood. Glucose is a major source of energy for most cells of the body, including those in the brain.

Review Date: 05/12/2009
Reviewed By: 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., Inc.