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Procedures for Glucose Tolerance Testing in Type 2 Diabetes

Individuals who have untreated diabetes have high blood glucose levels. One of the most common methods doctors use to aid in diagnosing an individual with diabetes is glucose tolerance testing--also known as OGTT, since the test is administered through the ingestion of an oral liquid.

  1. Type 2 Diabetes

    • According to the America Diabetes Association, Type 2 Diabetes is the form seen most often. In this type of diabetes, insulin is either not sufficiently produced by the body or it is not used by the cells as it should be, resulting in unusually high blood glucose (sugar) levels. These high blood glucose levels mean that the needed energy (sugar/glucose) for the body's cells is building up in the bloodstream instead of providing the body with the energy it needs to function.

    Pre-Testing Procedures and Diet

    • Individuals undergoing the OGTT method should not change their diet prior to the test period, with the exception of the 12-hour fast directly preceding the test. Maintaining a normal diet prior to the 12-hour fast will help your doctor in determine the normal glucose levels that occur in your bloodstream each day. Otherwise, a diet purposefully low in ingested sugar during the preceding days---and the resulting low glucose level reading---might cause him to not diagnose diabetes when it is present.

    Fasting Procedure

    • Fast from all foods and drinks (except water) for the 12 hours that directly precede the oral glucose tolerance test. Your doctor will advise if any of your medications will need to be stopped during the fast, but you will need to provide a list of your medicines first and seek his opinion on this matter.

    Test-day Procedures

    • According to the National Institutes of Health, the blood glucose level will be tested right before the test begins and every 30 to 60 minutes following the ingestion of the testing substance a patient is given to drink. The liquid she will be instructed to drink will be a type of glucose (sugar). The entire test time should be no more than three hours (see link in Resources Section).

    Test Symptoms and Results

    • Nausea and sweating can be symptoms experienced after ingestion of the glucose test drink. Pain or a prickling sensation, from the insertion of the needles used to withdraw blood for testing each 30- to 60-minute interval may also be experienced.

      A reading of less than 140 mg/dL two hours after the ingestion of the 75-gram oral glucose drink would indicate a "normal" range. Between 140 and 200 mg/dL after hour two would indicate prediabetes, according to the National Institutes of Health.

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