Fasting Blood Glucose
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.
Who is a candidate for the test?
If a doctor suspects a person may have diabetes
due to certain symptoms or risk factors, this test may be done.
How is the test performed?
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 After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test?
A person should have nothing to eat or drink other than water for at least 8 hours before this test.
What do the test results mean?
The fasting blood glucose in a person without diabetes
should be 99 mg/dL or less.
- If the result is higher than 99 mg/dL but less than 126 mg/dl, the diagnosis of impaired fasting glucose or pre-diabetes can be made.
- If the result is 126 mg/dL or higher, then another test should be done to confirm a diagnosis of diabetes.