Glucose Tolerance Test

Your doctor has asked that you have a Glucose Tolerance Test. This leaflet tells you what the test is and how you need to prepare for it.

What is a Glucose Tolerance Test?

In some people, the bodily system is unable to use glucose (sugar) properly. This may be obvious from a random check of the blood, but sometimes it needs to be checked in a formal test – the glucose tolerance test.

We would like you to have two blood tests: the first looks at the level of your blood glucose when you are fasting, and the second is done 2 hours later after you have had a special drink. In the test we measure how quickly the glucose disappears from your blood.

How is the test done?

You must have nothing to eat overnight and when you attend the Outpatients Department on the following morning, as indicated in your appointment letter, a sample of your blood will be taken.

If your blood glucose reading is above a certain level, it will be unnecessary to continue with the test. If your blood glucose reading is below this level, we will give you a drink containing glucose and take another blood sample from you two hours later. During this period you must not smoke or eat, but you may have a drink of water.

When will you get the result?

The results will be sent to your GP and he or she will give you the results when you next attend the surgery.

What will it mean to me if the test is abnormal?

If your test shows that your body does not clear glucose quickly enough, you may have Diabetes. Your doctor will decide which is the best course of treatment for you. Treatment could be a combination of diet, tablets, and/or insulin injections.

How should I prepare for the test?

Before the test:

1. For three days before the test, have your usual meals. Do not try to restrict or alter your normal eating pattern.
2. During the three days before the test, take your usual amount of exercise.
3. From 10.00 pm on the night before the test, you must eat nothing. You may drink only water. If you are a smoker, you must not smoke after 10.00 pm on the day before the test.
4. If you regularly take medicines, take them as usual. If any of these should be taken with food, it may be advisable to delay taking them until after you have had the test. If you are unsure about this, contact your doctor. Please bring a list of any medicines that you are taking and give the list to the person who does the test. (Some medicines can affect the test).
5. If you are a smoker, you must not smoke until after the test is completed. (Smoking can alter the results).

On the morning of the test:

6. Attend for your appointment as indicated in your appointment letter. As you are likely to have to stay for about two hours, you may wish to bring something with which to occupy yourself, such as a book.
7. A blood sample will be taken from your arm.
8. You will be asked to drink about 400ml of a Lucozade drink, which should be drunk within 5 minutes.
9. After 2 hours has elapsed, a second blood sample will be taken.
10. During this period you may drink water if you wish.
11. The two blood samples will then be sent to the laboratory for testing. A written report will be returned to your doctor’s surgery.
12. You may eat and drink normally after the test is over.

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