Glucose Tolerance Test (cont.)

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How are the results of the glucose tolerance test evaluated?

Glucose tolerance tests may lead to one of the following diagnoses:

  • Normal response: A person is said to have a normal response when the two hour glucose level is less than 140 mg/dl, and all values between 0 and 2 hours are less than 200 mg/dl.
  • Impaired glucose tolerance (IGT): A person is said to have impaired glucose tolerance when the fasting plasma glucose is less than 126 mg/dl and the two hour glucose level is between 140 and 199 mg/dl. This is sometimes referred to as "prediabetes" because people with IGT have a higher risk of developing diabetes.
  • Diabetes: A person has diabetes when two diagnostic tests done on different days show that the blood glucose level is high. This means either the two hour levels is greater than 200 mg/dl or the fasting glucose is noted as greater than 126 mg/dl. A glycosylated hemoglobin (HbA1c) level of 6.5% or more also supports a diagnosis of diabetes mellitus.
  • Diabetes during pregnancy: A pregnant woman has diabetes if she has a fasting plasma glucose of over 92 mg/dl, or a two hour glucose level greater than 153 mg/dl.

What about glucose tolerance testing during pregnancy?

As mentioned previously, the glucose tolerance test is used for the diagnosis of gestational diabetes (diabetes that develops during pregnancy). It may be used if there are equivocal fasting or random blood glucose results, or to screen for gestational diabetes in pregnant women between 24 to 28 weeks of gestation who are not known to have diabetes.

The test may also be used in the postpartum period to detect diabetes in women who had gestational diabetes during pregnancy. Women who had gestational diabetes do not always develop diabetes later in life, but they should undergo diabetes screening at least every three years throughout their life.

REFERENCES: Glucose Tolerance Testing. Glucose Tolerance Workup. Diabetes Mellitus During Pregnancy.

Medically Reviewed by a Doctor on 7/17/2014