Glucose Tolerance Test

  • Medical Author:
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Better Blood Sugar Balance

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.

Medically reviewed by a Board-Certified Family Practice Physician

REFERENCES:

MedscapeReference.com. Glucose Tolerance Testing.

MedscapeReference.com. Glucose Tolerance Workup.

MedscapeReference.com. Diabetes Mellitus During Pregnancy.

Medically Reviewed by a Doctor on 3/15/2016
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