Oral glucose tolerance test (OGTT)

Oral glucose tolerance test (OGTT) is a kind of laboratory test that measures patient’s glucose tolerance and sugar break down process. Doctor requests oral glucose tolerance test if you have diabetes symptoms, OGTT will help to diagnose the diabetes. With the result of oral glucose tolerance test, diabetes can be diagnosed or the result would be normal or may show the prediabetes; means you are a candidate for diabetes. A OGTT test is done during the pregnancy to monitor gestational diabetes, the test  procedure is a little different from normal.

How the Oral Glucose Tolerance Test is Performed ?

In OGTT a certain amount of sugar will be loaded into your body and your body’s answer will be monitored.

Your doctor may request you to fast for 8-10 hours before your oral glucose tolerance test, you can only drink water during fasting.

At the beginning of the oral glucose tolerance test a blood sample is taken to analyse fasting blood glucose level.

You will be given 300 mL of water that contains 75 gr of glucose to drink. Some lemon juice may be added to make drinking easier.

After 2 hours from drinking glucose, your blood will be taken again, don’t eat,drink or smoke at this waiting period.

Oral glucose tolerance test

Evaluation of Oral Glucose Tolerance Test

Patient’s fasting blood glucose level and the answer to glucose load will be determined with the taken blood samples.

If glucose level is higher than 200 mg/dL in 2. hour blood sample this means you have diabetes.

If glucose level between 140-200 mg/dL in second blood sample this means you have impaired glucose tolerance and your doctor will explain you this is prediabetes means you are under the risk of diabetes and some precautions are needed to prevent diabetes. Your doctor will give you instructions about your lifestyle to prevent from diabetes. For example walking for half an hour even may be useful or following your diet carefully.

The results under 140 mg/dL after 2 hours mean you are normal and you don’t have diabetes.

Oral glucose tolerance test may change for different countries, after glucose load, 2 blood samples may be taken after 1 hour and 2 hours or an urine sample may be needed for an urinalysis during the test.


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