How To Prepare
Fasting blood sugar (FBS)
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.
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 glycohemoglobin 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
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
There is very little risk of a problem from
having blood drawn from a vein.
- You may develop a small bruise at the puncture site. You can
reduce the risk of bruising by keeping pressure on the site for several minutes
after the needle is withdrawn.
- In rare cases, the vein may become
inflamed after the blood sample is taken. This condition is called phlebitis
and is usually treated with a warm compress applied several times
- Continued bleeding can be a problem for people with bleeding
disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can
also make bleeding more likely. If you have bleeding or clotting problems, or
if you take blood-thinning medicine, tell your health professional before your
blood is drawn.