An oral glucose tolerance test may be performed on healthy individuals, people with diabetes or pregnant women to observe the effects on blood sugar levels following the administration of glucose. The test may assist physicians in making a diagnosis of impaired glucose tolerance or diabetes. Depending on each specific patient's circumstances, the test is administered following a specific pathway and the results are interpreted accordingly.
Fasting Blood Glucose
Step 1
Prepare by fasting for 8 to 10 hours before your clinic appointment, or as directed by your physician.
Step 2
A member of the clinic staff will draw a sample of your blood and submit it for analysis.
Step 3
The results of fasting blood glucose are analyzed. Fasting blood glucose levels between 70-99 mg/dL are normal. Levels between 100-125 mg/dL are considered impaired fasting blood glucose and may indicate pre-diabetes. Levels greater than 126 mg/dL on more than one occasion may indicate the presence of diabetes.
Step 4
If the fasting glucose test indicates the presence of pre-diabetes or diabetes, you may be asked to complete an additional test called the oral glucose tolerance test.
Oral Glucose Tolerance Test for Non-Pregnant Patients
Step 1
Consume a sweet tasting solution that contains 75 g of glucose.
Step 2
You will have blood drawn 2 hours after drinking the solution.
Step 3
The results of the glucose tolerance test are analyzed. Blood glucose levels between less than 140 mg/dL are normal. Levels between 140 and 200 mg/dL are considered impaired blood glucose and may indicate pre-diabetes. Levels greater than 200 mg/dL on more than one occasion may indicate the presence of diabetes.
Oral Glucose Tolerance Test for Pregnant Women
Step 1
You will have a gestational diabetes screen by having blood drawn 1 hour after consuming a solution containing 50 g of glucose. If the glucose level at that time is above 140 mg/dL, you may be asked to make an additional appointment for the oral glucose tolerance test for gestational diabetes.
Step 2
You will have blood drawn for a fasting blood glucose measurement, with a target of 95 mg/dL. You will then consume a solution containing 100 g of glucose. Blood glucose levels will be drawn at the 1 hour and 2 hour marks. In some cases, you may only consume 75 g of glucose. In those instances, levels will be drawn at the 1 hour, 2 hour and 3 hour marks.
Step 3
The results of your oral glucose tolerance test are analyzed. The target glucose levels are 180 mg/dL at 1 hour, 155 mg/dL at 2 hours and 140 mg/dL at 3 hours. If two or more results, including the fasting blood glucose measurement, exceed the target values, a diagnosis of gestational diabetes is made.
Tips and Warnings
- During fasting periods, it is appropriate to drink water but not any liquids that contain sugar.
- Certain medications and health conditions can cause impaired glucose tolerance and interfere with test results. Always make your physician aware of any known health conditions and medications you are taking.
Things You'll Need
- Determine what category of patient you are (healthy, diabetic, or pregnant)
- Clinic appointment with physician or diabetes specialist
- Appropriate time for fasting before tests
- Appropriate time for tests to be administered
- List of current medications and health conditions
