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Oral glucose tolerance test

Oral Glucose Tolerance Test
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What is an oral glucose tolerance test (OGTT)?

An oral glucose tolerance test (OGTT) measures how well your body uses sugar (glucose). It can be used to find prediabetes and diabetes. It's done most often to screen for diabetes during pregnancy (gestational diabetes).

Why is an oral glucose tolerance test done?

The oral glucose tolerance test (OGTT) is done to:

  • Check pregnant women for gestational diabetes. You have an increased chance of getting gestational diabetes if you have had gestational diabetes during a previous pregnancy.
  • Check for prediabetes and diabetes.

How is an oral glucose tolerance test (OGTT) done?

  • A blood sample is taken when you arrive for the test. This is your fasting blood glucose value. It will be compared to other glucose values in your blood.
  • You will drink a small cup of very sweet liquid that contains 75 or 100 grams of glucose.
  • You will have more blood tests over 1 to 3 hours.
  • Since activity can affect test results, you will be asked to sit quietly during the entire test. Do not eat during the test. You may drink water during this time.

How do you prepare for an oral glucose tolerance test (OGTT)?

  • Tell your doctor about all the prescription and nonprescription medicines you are taking. You may be told to stop taking certain medicines before the test.
  • Do not eat, drink, smoke, or do strenuous exercise for at least 8 hours before your first blood sample is taken. (You can drink water before the test.)

What do the results of an oral glucose tolerance test (OGTT) mean?

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

High values

High glucose levels may be caused by:

  • Diabetes.
  • Gestational diabetes.
  • Hyperthyroidism.
  • Some medicines, such as corticosteroids, niacin, phenytoin (Dilantin), some diuretics, and some medicines used to treat high blood pressure, HIV, or AIDS.
  • Large amounts of the hormone cortisol in the blood (Cushing's syndrome).
  • Inherited diseases, such as hemochromatosis.
  • Pheochromocytoma.

Low values

Low glucose levels may be caused by:

  • Certain medicines, such as medicines used to treat diabetes, some blood pressure medicines (such as propranolol), and some medicines for depression (such as citalopram).
  • Decreased production of the hormones cortisol and aldosterone (Addison's disease).
  • Problems with the thyroid gland or an underactive pituitary gland.
  • A tumor or other problems of the pancreas.
  • Liver disease.

Many conditions can change blood glucose levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.

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The content above contains general health information provided by Healthwise, Incorporated, and reviewed by its medical experts. This content should not replace the advice of your healthcare provider. Not all treatments or services described are offered as services by us. For recommended treatments, please consult your healthcare provider.