An oral glucose tolerance test (OGTT) is one of the most common glucose tolerance tests and works by confirming whether an individual has difficulty processing sugar, which could indicate diabetes. During the test your blood glucose level will be tested before and after you drink a glucose liquid to measure how quickly your body metabolises the glucose.

On the day of the test, you will be asked not to eat or drink anything after midnight. Once in the clinic, you will have a series of three blood and urine tests - one blood sample and urine sample before the glucose drink, one blood sample and urine sample one hour after and a third blood sample and urine sample an hour later. During the test, you will have blood collected 3 times over 2 hours. You will be asked to rest in the waiting room during the test. Smoking, eating and drinking must be avoided.

The glucose levels of a person who doesn’t suffer from diabetes will rise quickly after drinking the glucose drink and then fall again just as quickly. If a person has diabetes, their glucose levels will rise higher than a person without diabetes and then come back down much more slowly, demonstrating high blood glucose levels in their blood.