Glucose tolerance test (GTT)
Significance
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Done to confirm or rule out diabetes. |
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Can also indicate those at risk of developing diabetes in future |
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Procedure
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Person to be tested must be on their usual diet ,exercise and routine schedule for at least 3 days prior to the test. |
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Test be carried out in the morning after fasting for 8 hours; blood is collected in the fasting state. |
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75 grams of anhydrous glucose ( for children the dose is 1.75 grams of glucose per kg of body weight up to maximum of 75 grams.) is given orally; this may be dissolved in water to avoid nausea; it may be flavored with a little lime to make it more palatable; the glucose solution should be ingested within 4-5 minutes. If glucose monohydrate ( which is the form of glucose most commonly available in the market) is used,82.5 gms. must be administered. |
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The person must rest throughout the test. |
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Smoking must not be permitted during the test. |
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A note be made of any factor which may interfere with the correct interpretation of the test (e.g. medications, in activity, infections etc.) |
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Blood is collected 2 hours after glucose ingestion. |
The results are interpreted according to WHO criteria.
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Impaired Glucose Tolerance Test ( IGT)
Many patients in this category will go on to have diabetes.
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Many IGT patients show associated problems like hypertension, lipid disorders, high uric acid, obesity etc, which merit treatment.
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IGT is a risk factor for the development of macro vascular disease.
Impaired Fasting Glycemia (I.F.G)
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Recently introduced to delineate persons in whom only the fasting blood glucose has been done ,but who do not come in the normal or diabetic category. |
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It has been proposed that the diagnosis of diabetes can be made from a fasting blood glucose level only and that it may not be necessary to do a complete GTT. |
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However these patients with I.F.G. should be confirmed with a complete glucose tolerance test ,if feasible. |
Normal result
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Values not falling within any of the above categories signifies a normal tolerance to glucose. |
A negative test only shows that the patient is not diabetic at the time of testing; it does not mean that he will never develop diabetes; such persons must have an annual checkup.