You will be asked not to eat anything for about four hours beforehand, and not to drink for about two hours. Your stomach needs to be empty so that your doctor can get as clear a picture as possible.

If you are diabetic, you will get some special instructions to follow.

If you are taking prescribed medicines, take them as normal with sips of water. However, ulcer-healing drugs (eg Tagamet, Zantac) need to be stopped for four weeks before the test.

The hospital will send you full details with your appointment letter. If in doubt, please ask.