What is the 3-Hour Glucose Tolerance Test GTT?
The 3-hour glucose tolerance test is used during pregnancy to rule out or diagnose gestational diabetes. Typically, the 1-hour glucose tolerance test is given first with the 3-hour glucose tolerance test reserved for women who fail the initial test.
Activity and diet need to be normal for at least three days prior to the test. Women fast the night before reporting to the lab. Upon arrival, a fasting blood draw is performed. After the initial blood draw, 75 to 100 grams of glucose solution are consumed. One, two and three hours after the glucose solution has been consumed, lab techs draw another sample of blood. If at least two of the normal values are exceeded during the test, gestational diabetes is diagnosed.
Normal Value Range
- Fasting Values: 95 mg/dL or 5.3 mmol/L
- 1 Hour Values: 180 mg/dL or 10 mmol/L
- 2 Hour Values: 155 mg/dL or 8.6 mmol/L
- 3 Hour Values: 140 mg/dL or 7.8 mmol/L