This test measures the amount of glucose in the blood. It is called fasting because the level is measured at least 8 hours after a person last ate or drank anything.
If a doctor suspects a person may have diabetes or pre-diabetes due to certain symptoms or risk factors, this test may be done.
In order to measure the amount of glucose in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a rubber tube called a tourniquet is tied around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
A person should have nothing to eat or drink other than water for at least 8 hours before this test.
The fasting blood glucose in a person without diabetes should be 110 mg/dL or less.
Author:Melinda Ratini, DO, MS
Date Written:
Editor:Crist, Gayle P., MS, BA
Edit Date:06/12/02
Reviewer:Kathleen A. MacNaughton, RN, BSN
Date Reviewed:06/11/02