What is the oral glucose tolerance test?
Diabetes mellitus (DM) is a condition that affects the body’s ability to regulate the level of glucose in the blood. Glucose is the main form of sugar in the blood. The body breaks down food into glucose, or sugar and uses it as a source of energy. In healthy people insulin helps to regulate the glucose or the blood sugar levels. Insulin is a hormone produced by the pancreas that is a long, thin organ located behind the stomach against the back.

In diabetics, the body does not produce enough insulin or does not use the produced insulin effectively. This results in high level of glucose in the blood and this condition is known as hyperglycaemia. There are several blood sugar tests used for diagnosis of diabetes mellitus.

What does the glucose tolerance test measure?
The classic oral glucose tolerance test measures blood glucose levels five times over a period of 3 hours. Some physicians simply get a baseline blood sample followed by a sample 2 hours after drinking the glucose solution. In a person without diabetes, the glucose levels rise and then fall quickly. In someone with diabetes, glucose levels rise higher than normal and fail to come back down as fast.

People with glucose levels between normal and diabetic have impaired glucose tolerance (IGT). People with impaired glucose tolerance do not have diabetes. Each year, 1%-5% of people whose test results show impaired glucose tolerance actually develop diabetes. Weight loss and exercise may help people with impaired glucose tolerance return their glucose levels to normal. In addition, some physicians advocate the use of medications, such as metformin (Glucophage), to help prevent/delay the onset of overt diabetes. Recent studies have shown that impaired glucose tolerance itself may be a risk factor for the development of heart disease, and whether impaired glucose tolerance turns out to be an entity that deserves treatment itself is something that physicians are currently debating.