The OGTT evaluates how the body manages glucose after a meal. Glucose is a type of sugar produced when the body breaks down carbohydrates consumed in food. Some of the glucose will be used for energy; the rest will be stored for future use.
The amount of glucose in your blood is controlled by the hormones insulin and glucagon. If you have too much, the pancreas secretes insulin to help cells absorb and store glucose. If you have too little, the pancreas secretes glucagon so that stored glucose can be released back into the bloodstream.
Under normal circumstances, the body will be able to maintain the ideal balance of blood glucose. However, if any parts of the system are impaired, glucose can rapidly accumulate, leading to high blood sugar (hyperglycemia) and diabetes.
The OGTT is a highly sensitive test that can detect imbalances that other tests miss. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) recommends the OGTT for the following purposes:
Screening and diagnosis of prediabetes or impaired glucose tolerance (IGT)
Screening and diagnosis of type 2 diabetes
Screening and diagnosis of gestational diabetes
The OGTT is only used for diagnosis and screening. It has no role in the monitoring of diabetes or prediabetes.
Among its other uses, the OGTT can be ordered to diagnose reactive hypoglycemia (in which blood sugar drops after eating), acromegaly (an overactive pituitary gland), beta cell dysfunction (in which insulin is not being secreted), and rare disorders affecting carbohydrate metabolism (such as hereditary fructose intolerance).