Why It Is Done
Blood glucose tests are done to:
- Check for prediabetes and diabetes.
treatment of diabetes.
- Check for diabetes that occurs during
pregnancy (gestational diabetes).
- Determine if an abnormally low
blood sugar level (hypoglycemia) is present. A test to
measure blood levels of insulin and a protein called C-peptide may be done
along with a blood glucose test to determine the cause of hypoglycemia. To learn more, see the topic
How To Prepare
Fasting blood sugar (FBS)
This is one of several tests that is used to diagnose diabetes. For a fasting blood
sugar test, do not eat or drink anything other than water for at least 8 hours
before the blood sample is taken.
If you have diabetes, you may be
asked to wait until you have had your blood tested before taking your morning
dose of insulin or diabetes medicine. You may have a random blood sugar test instead, which will not require an 8-hour fast.
2-hour postprandial blood sugar
2-hour postprandial test, start eating a meal exactly 2 hours
before the blood sample is taken. A
home blood sugar test is the most common way to check
2-hour postprandial blood sugar levels.
Random blood sugar (RBS) and hemoglobin A1c
No special preparation is
required before having a random blood sugar or A1c test.
Oral glucose tolerance test
For an oral glucose tolerance test, you'll need to follow a special diet for 3 days before the test. And do not eat, drink, smoke, or exercise strenuously for at least 8 hours before your first blood sample is taken.
To learn more about how to prepare for this test, see Oral Glucose Tolerance Test.
Talk to your doctor about any concerns
you have regarding the need for the test, its risks, how it will be done, or
what the results may mean.
To help you understand the importance of this
test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional taking a sample
of your blood will:
- Wrap an elastic band around your upper arm to stop the flow of
blood. This makes the veins below the band larger so it is easier to put a
needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Apply a gauze pad or cotton ball over the needle site as
the needle is removed.
- Apply pressure to the site and then a