laboratory values, gestational diabetes (GDM), glucose challenge test (GCT and GTT)

What is the 2-Hour Glucose Tolerance Test?


In some cases, the 2-hour glucose tolerance test may be used in place of the 1-hour glucose tolerance test during pregnancy, and the protocol is basically the same. You fast overnight and then go the lab in the morning to give a blood sample. Then, you drink a 75-gram glucose solution. One hour and two hours after consumption blood draws are taken to measure blood glucose.

If levels are higher than normal at any stage of the test, additional testing may be ordered to rule out, or definitively diagnose gestational diabetes.

The test requires at least three days of normal food consumption and activity before fasting. Smoking is not allowed during the test as results may be affected.

Normal Value Range

  • Fasting Values: 92 mg/dL or 5.1 mmol/L
  • 1-Hour Values: 180 mg/dL or 10 mmol/L
  • 2-Hour Values: 153 mg/dL or 8.5 mmol/L

* Values are not affected by pregnancy

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