Oral Glucose Tolerance Test

Glucose Challenge Test, Glucose Tolerance Test, OGTT (Oral Glucose Tolerance Test)

How It Is Done

Glucose challenge screening test for gestational diabetes

• You will be asked to drink a sweet liquid containing glucose. It is best to drink the liquid quickly.
• A blood sample will be collected 1 hour after you drink the glucose. Normally, blood glucose levels peak within an hour and then begin to drop.

If the screening test results indicate that you may have gestational diabetes, the complete glucose tolerance diagnostic test may be done.

Glucose tolerance diagnostic test

On the day of testing, the following steps will be done:

• A blood sample will be collected when you arrive. This is your fasting blood glucose value. It provides a baseline for comparing other glucose values.
• You will be asked to drink a sweet liquid containing a measured amount of glucose. It is best to drink the liquid quickly. For the standard glucose tolerance test, you will drink 75 g (3 oz) to 100 g (4 oz); pregnant women drink 100 g (4 oz) of glucose.
• Blood samples will be collected at timed intervals of 1, 2, and 3 hours after you drink the glucose. Blood samples may also be taken as soon as 30 minutes to more than 3 hours after you drink the glucose.

Glucose challenge screening test for polycystic ovary syndrome (PCOS)

• You will be asked to drink a sweet liquid containing glucose. It is best to drink the liquid quickly.
• A blood sample will be collected 2 hours hour after you drink the glucose. Normally, blood glucose levels peak within an hour and then begin to drop.

If the screening test results indicate that you may have diabetes, other tests may be needed.

Blood test

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 alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Apply a gauze pad or cotton ball over the needle site as the needle is removed.
• Apply pressure to the site and then a bandage.

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Author:	Caroline Rea, RN, BS, MS	Last Updated: September 14, 2007
Medical Review:	Caroline S. Rhoads, MD - Internal Medicine Alan C. Dalkin, MD - Endocrinology Andrew Swan, MD, CCFP, FCFP - Family Medicine
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