Also known as oral glucose tolerance test (OGTT). This laboratory test is used to detect gestational diabetes, diabetes that has not yet caused complaints, and the condition that precedes it (decreased glucose tolerance), and to assess carbohydrate metabolism.
OGTT should not be performed in case of diabetics if a diagnosis of diabetes can be made based on fasting or postprandial blood glucose.
Before the glucose tolerance test, it is advisable to consume a balanced meal containing at least 150g of carbohydrates per day.
The test is performed in the morning on an empty stomach with two samples. First, a fasting blood test followed by a blood sugar level check. If the measured value is below 7.00 mmol/l, the test can be performed, at which point the patient should consume a sweet solution containing 75g of glucose. Then, after 120 minutes, a second blood sample is taken, from which glucose tolerance can be determined after checking the blood sugar level.
In case of normal metabolic function, the 120-minute value should return to a level around the empty stomach value. If it remains elevated, a carbohydrate metabolism disorder may be suspected.
Based on the blood glucose values measured 2 hours later, we speak of a normal glucose tolerance of less than 7.8 mmol/l, a decreased glucose tolerance of 7.8-11.0 mmol/l, and a value above 11.0 mmol/l we talk about diabetes.