Oral Glucose Tolerance Tests

The purpose of the oral glucose tolerance test is to measure the body's ability to use a type of sugar, called glucose. Glucose is the body's main source of energy. An OGTT can be used to diagnose prediabetes and diabetes. An OGTT is most commonly done to check for diabetes that occurs with pregnancy, called gestational diabetes.

How To Prepare - 1 hour test

  1. Eat a meal low in carbohydrates before this test. Example of foods to eat for breakfast would be eggs, cheese, bacon and or sausage. Avoid breads, cereals and fruit juices. Example of foods for lunch would be lettuce/salad with any kind of meat. Green beans, broccoli and any leafy vegetable. Avoid fried foods, no bread, soft drinks with sugar or sweet tea.
  2. 1 1/2 - 2 hours after eating, drink the entire 59 gram glucola drink.
  3. Be at the office 30 minutes after finishing the cola. This is to insure that you are at the clinic on time for your blood work which will be drawn 1 hour after drinking the cola.
  4. When you check in at the fron desk, be sure and tell the receptionist what time you finished drinking the cola.

How to Prepare - 3 hour test

If your doctor would like to see additional testing, based on your results from the 1 hour test, you may be asked to have a 3 hour OGTT. It is important to follow all of the instructions very carefully, as it will affect the results of the test.

When you arrive at the office a sample or baseline glucose test will be run and used for comparing other glucose values. You will be asked to drink a sweet liquid containing a measured amount of glucose, it is best to drink it quickly. Then blood samples will be collected at timed intervals of 1,2, and 3 hours after you drink the glucose.

Here is the best method of preparation:

  1. Eat a balanced diet that contains at least 150 grams of carbohydrates per day for 3 days before the test. Fruits, breads, cereal, rice, crackers, and starchy vegetables such as potatoes, beans and corn are good sources of carbohydrates.
  2. Do not eat, drink, smoke, or exercise strenuously for at least 8 hours before your first blood sample is taken.
  3. Tell your doctor about all prescription and nonprescription medicines you are taking. You may be instructed to stop taking certain medicines before the test.
  4. The OGTT may take up to 4 hours. Since activity can interfere with test results, you will be asked to sit quietly during the entire test. Do not eat during the test. You may drink only water during this time.