The diagnosis of type 2 diabetes

The oral glucose tolerance test (OGTT) is used to check the blood glucose level and is carried out if diabetes mellitus is suspected. It shows how well sugar in food can be absorbed by the cells in the body. With a normal metabolism, eating carbohydrates leads to an increase in blood glucose concentration, which triggers the release of insulin from the pancreas. The insulin causes the cells in the body to absorb glucose, which then promptly reduces the blood glucose level. With type 2 diabetes, the pancreas releases too little insulin, or the released insulin does not act properly in the cells of the body. This leads to a higher and more sustained increase in the blood glucose level.

• The OGTT is done with the patient sitting or lying down. The patient may not eat or smoke for 8 to 12 hours beforehand.
• Three days before the OGTT, a high carbohydrate diet should be followed (at least 150 grams of carbohydrate at day).
• To begin the test (time 0), the patient drinks the premixed glucose solution with 75 grams of glucose within 5 minutes. During the 2-hour measuring period, blood is taken at 0 minutes and at 120 minutes to determine the blood glucose level.

A normal glucose level is defined as a fasting glucose level (time 0) of less than 100 mg/dl (less than 5.6 mmol/l) and an 2-hour OGTT blood glucose level of less than 140 mg/dl (less than 7.8 mmol/l), measured in venous plasma. Fasting blood glucose levels of 126 mg/dl (7.0 mmol/l) or higher or 2-hour OGTT values of 200 mg/dl (11.1 mmol/l) or higher means that the patient has diabetes mellitus.

People with a blood glucose level above the normal glucose tolerance, but below the diabetes diagnosis have a higher risk of developing diabetes. This transition range is called prediabetes and includes impaired fasting glucose (fasting blood glucose of 100 mg/dl or higher (5.6 mmol/l or higher) and less than 126 mg/dl (less than 7.0 mmol/l)) and impaired glucose tolerance (2-hour OGTT of 140 mg/dl or higher (7.8 mmol/l or higher) and less than 200 mg/dl (less than 11.1 mmol/l)).