Glucose Tolerance Test
Alternate Names : Oral Glucose Tolerance Test, OGTT, GTT
This test is primarily used to measure how well the body can use,
or metabolize, glucose. Glucose is the main form of sugar in the body.
Who is a candidate for the test?
The test is done when a doctor thinks a person has diabetes mellitus,
which results in a high blood glucose level. It is also advised in all pregnant women to screen for
diabetes of pregnancy.
How is the test performed?
In the glucose tolerance test, samples of a person's blood are
measured at certain times after the person drinks a solution of glucose in
A blood sample is first taken before the person drinks a sweet drink.
Then, samples are taken again at certain times after drinking it. Common times that are used include:
To measure glucose in the blood, a sample of blood is needed.
This is most often drawn from a vein in the forearm or hand. To do this, the skin
over the vein is first cleaned with an antiseptic. Next, a rubber tube called a
tourniquet is wrapped around the upper arm. This enlarges the veins in the
lower arm and restricts blood flow through them. A very thin 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. It is then sent to the
laboratory for testing. After the needle is withdrawn, the puncture site
is covered for a short time to prevent bleeding.
In some cases, urine samples may also be used to look for extra
glucose. Samples of midstream urine, that is, not at the beginning and not at
the end, are collected at the same time intervals as the blood samples are taken.