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What is the oral glucose tolerance test?
Why is it done?
How is it done?
What are the normal values?
What are the abnormal values?
Written by : DoctorNDTV Team
  • 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.
  • Why is it done?

    Diabetes mellitus is diagnosed based on a high level of glucose or sugar in the blood. The oral glucose tolerance test is the preferred way to diagnose pregnancy or stress- induced diabetes.
  • How is it done?

    In this test the patient fasts overnight. Out-patients should rest for at least half ann hour before starting the test and should remain seated and refrain from smoking during the test. The patient is asked to drink glucose water. Thereafter samples of blood are collected at an interval of every half an hour for 2 hours, and their glucose content is estimated.
  • What are the normal values?

    If a person does not have diabetes, the glucose levels will rise upto 180mg/ml and then fall to normal levels within 2 hours.

    Glucose concentration mmol/l (mg/100ml)


    Fasting < 100 mg/100ml

    2 hours after glucose < 120 mg/100ml
  • What are the abnormal values?

    When a person has diabetes, glucose levels will rise higher than normal and fail to come down.

    Glucose concentration mmol/l (mg/100ml)


    Fasting > 120

    2 hours after glucose > 180

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